Support local Modrinth modpack files (#2594)

Dockerfile

@@ -49,7 +49,7 @@ RUN easy-add --var os=${TARGETOS} --var arch=${TARGETARCH}${TARGETVARIANT} \
   --var version=${MC_SERVER_RUNNER_VERSION} --var app=mc-server-runner --file {{.app}} \
   --from ${GITHUB_BASEURL}/itzg/{{.app}}/releases/download/{{.version}}/{{.app}}_{{.version}}_{{.os}}_{{.arch}}.tar.gz
 
-ARG MC_HELPER_VERSION=1.37.6
+ARG MC_HELPER_VERSION=1.37.7
 ARG MC_HELPER_BASE_URL=${GITHUB_BASEURL}/itzg/mc-image-helper/releases/download/${MC_HELPER_VERSION}
 # used for cache busting local copy of mc-image-helper
 ARG MC_HELPER_REV=1

docs/types-and-platforms/mod-platforms/modrinth-modpacks.md

@@ -9,11 +9,17 @@ The desired modpack project is specified with the `MODRINTH_MODPACK` environment
 - The project "slug", which is located in the URL shown here:
 
   ![](../../img/modrinth-project-slug.drawio.png)
+
 - The project ID, which is located in the bottom of the left panel, shown here
 
   ![](../../img/modrinth-project-id.drawio.png)
+
 - The project page URL, such as <https://modrinth.com/modpack/cobblemon-fabric>. As described below, this can further be the page URL of a modpack's version page.
 
+- A custom URL of a hosted [mrpack file](https://support.modrinth.com/en/articles/8802351-modrinth-modpack-format-mrpack)
+
+- The container path to a local [mrpack file](https://support.modrinth.com/en/articles/8802351-modrinth-modpack-format-mrpack)
+
 ## Modpack version
 
 The automatic modpack version resolving can be narrowed in a few ways:

examples/modrinth/local-modpack/docker-compose.yml

@@ -0,0 +1,15 @@
+services:
+  mc:
+    image: itzg/minecraft-server
+    environment:
+      EULA: true
+      MOD_PLATFORM: MODRINTH
+      # Download the mrpack file from https://modrinth.com/modpack/cobblemon-fabric/version/1.4.1 and place in
+      # modpacks directory next to this compose file.
+      MODRINTH_MODPACK: /modpacks/Cobblemon Modpack [Fabric] 1.4.1.mrpack
+    volumes:
+      - mc-data:/data
+      - ./modpacks:/modpacks:ro
+
+volumes:
+  mc-data: {}