chore(deps): update dependency caddyserver/caddy to v2.4.0 (#29)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [caddyserver/caddy](https://github.com/caddyserver/caddy) | minor | `v2.3.0` -> `v2.4.0` |

---

### Release Notes

<details>
<summary>caddyserver/caddy</summary>

### [`v2.4.0`](https://github.com/caddyserver/caddy/releases/v2.4.0)

[Compare Source](https://github.com/caddyserver/caddy/compare/v2.3.0...v2.4.0)

Caddy v2.4.0 is our first stable release of 2021, ushering in over 110 patches including new features and bug fixes. Thank you to the many contributors who helped make this possible!

Highlights:

-   **Secure remote management.** You can now [enable secure remote access](https://caddyserver.com/docs/json/admin/remote/) to Caddy's [admin API](https://caddyserver.com/docs/api)! It uses TLS mutual authentication, and you can even define permissions for different users. PR [#&#8203;3994](https://github.com/caddyserver/caddy/issues/3994)
-   **Config pull at start.** Caddy can be configured to [load a different config at startup](https://caddyserver.com/docs/json/admin/config/load/). This is useful if your config is federated through a separate system that doesn't have the ability to push configs to Caddy. This feature is modular, so configurations can be loaded different ways! PR [#&#8203;3994](https://github.com/caddyserver/caddy/issues/3994)
-   **Server identity management.** Caddy can [automatically manage its own server identity certificate](https://caddyserver.com/docs/json/admin/identity/), which can be used when negotiating TLS connections with peers. This is required when enabling the secure admin API. PR [#&#8203;3994](https://github.com/caddyserver/caddy/issues/3994)
-   **Self-upgrade command.** The [new `caddy upgrade` command](https://caddyserver.com/docs/command-line#caddy-upgrade) will replace the current Caddy binary with an upgraded one from our website, with all the same modules installed, including third-party plugins that are registered on our site! (We can use this code to add/remove modules later, too.)
-   **Configure other apps from the HTTP Caddyfile.** The global options block of the Caddyfile now allows configuration of Caddy apps other than HTTP (for example, [dynamic_dns](https://github.com/mholt/caddy-dynamicdns) to keep DNS records pointed at your server with a dynamic IP address).
-   **Caddyfile `fmt` lint check.** When running with a Caddyfile, Caddy will emit a warning if the Caddyfile is not formatted with `caddy fmt`.
-   **New `abort` directive.** [The `abort` directive](https://caddyserver.com/docs/caddyfile/directives/abort) is a special case of the `static_response` HTTP handler that _prevents_ an HTTP response by aborting the handler chain immediately and forcefully closing the connection.
-   **New `error` directive.** [The `error` directive](https://caddyserver.com/docs/caddyfile/directives/error) returns internal error values in the HTTP handler chain, as if an HTTP error had occurred, causing your error routes to be invoked.
-   **Configure response interception from Caddyfile.** The reverse_proxy is capable of intercepting responses from the backend, and [now this is exposed in the Caddyfile with `handle_response`](https://caddyserver.com/docs/caddyfile/directives/reverse_proxy#intercepting-responses).
-   **Better `caddy list-modules` output.** Now modules are organized by standard and non-standard modules, so you can easily see if a Caddy build has been customized.
-   **Configure logging from Caddyfile.** The process logs can now be [configured from the global options](https://caddyserver.com/docs/caddyfile/options#log) of the Caddyfile.
-   **Better content negotiation.** [The file server can now be configured](https://caddyserver.com/docs/modules/http.handlers.file_server#precompressed) to serve precompressed sidecar files, and content encoding preferences are better configured and honored.
-   **Dark mode in directory listings.** The file server's "browse" file listings now has a dark mode.
-   **⚠️ Removed the `logfmt` log encoder.** It was broken anyways, and its deprecation has been warned in previous releases.
-   **⚠️ Deprecated `common_log` format.** It will be removed in a future release. Issue [#&#8203;4148](https://github.com/caddyserver/caddy/issues/4148)
-   **⚠️ Deprecated `health_path` in `reverse_proxy` directive.** It has been replaced with `health_uri` and will be removed in the future.
-   **Numerous bug fixes and improvements.** Thanks for the detailed, helpful bug reports! We appreciate your collaboration in making Caddy better.

#### New content for sponsors

I've started writing high-quality, in-depth chatpers about how to get the most out of Caddy in my new [Expert Caddy](https://matt.life/expert-caddy) series, exclusively for sponsors! If you or your company are sponsoring, you can have access to this content, which I'll continue adding to over time.

If you aren't sponsoring yet, [please do so](https://github.com/sponsors/mholt)! Sponsorships fund my full-time development of Caddy, and that's especially vital if your business relies on Caddy.

#### Changelog (since RC 1)

For a detailed list of all commits since v2.3.0, please refer to prior pre-release changelogs.

[`bc22102`](https://github.com/caddyserver/caddy/commit/bc221024) caddyfile: Fix `caddy fmt` nesting not decrementing ([#&#8203;4157](https://github.com/caddyserver/caddy/issues/4157))
[`d4b2f1b`](https://github.com/caddyserver/caddy/commit/d4b2f1bc) caddyhttp&#x3A; Fix fallback for the error handler chain ([#&#8203;4131](https://github.com/caddyserver/caddy/issues/4131))
[`61642b7`](https://github.com/caddyserver/caddy/commit/61642b76) caddytls: Run replacer on ask URL, for env vars ([#&#8203;4154](https://github.com/caddyserver/caddy/issues/4154))
[`7776471`](https://github.com/caddyserver/caddy/commit/77764714) encode: Default to order the formats are enabled for `prefer` in Caddyfile ([#&#8203;4151](https://github.com/caddyserver/caddy/issues/4151))
[`f5db41c`](https://github.com/caddyserver/caddy/commit/f5db41ce) encode: Drop `prefer` from Caddyfile ([#&#8203;4156](https://github.com/caddyserver/caddy/issues/4156))
[`74f5d66`](https://github.com/caddyserver/caddy/commit/74f5d66c) fileserver: Fix `file` matcher with empty `try_files` ([#&#8203;4147](https://github.com/caddyserver/caddy/issues/4147))
[`3cf443f`](https://github.com/caddyserver/caddy/commit/3cf443f0) httpcaddyfile: Add `grace_period` global option ([#&#8203;4152](https://github.com/caddyserver/caddy/issues/4152))
[`a17c3b5`](https://github.com/caddyserver/caddy/commit/a17c3b56) reverseproxy: Minor logging improvements

</details>

---

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---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).

Reviewed-on: docker/link-validator#29
Co-authored-by: Renovator Bot <renovator@rknet.org>
Co-committed-by: Renovator Bot <renovator@rknet.org>

Dockerfile

@@ -11,7 +11,7 @@ ARG BUILD_VERSION
 # renovate: datasource=npm depName=broken-link-checker
 ENV BLC_VERSION="${BUILD_VERSION:-0.7.8}"
 # renovate: datasource=github-releases depName=caddyserver/caddy
-ENV CADDY_VERSION="${CADDY_VERSION:-v2.3.0}"
+ENV CADDY_VERSION="${CADDY_VERSION:-v2.4.0}"
 
 ENV LINK_VALIDATOR_BASE_DIR=/drone/src \
     LINK_VALIDATOR_SERVER_PORT=80 \