Add support for Modrinth projects file (#3506)

docs/mods-and-plugins/modrinth.md

@@ -12,6 +12,8 @@
   Also, a specific version (or release type) can be declared adding a colon and then the version id, version number/name, or release type after the project slug. The version ID or number can be found in the 'Metadata' section. Valid release types are `release`, `beta`, `alpha`.
   
   To select a datapack from a Modrinth project, prefix the entry with "datapack:". When running a vanilla server, this is optional since only datapacks will be available for vanilla servers to select.
+  
+  You can also reference a file containing project entries by prefixing the **container path** path with `@`.
         
   | Description                     | Example projects entry                                |
   |---------------------------------|-------------------------------------------------------|
@@ -21,6 +23,24 @@
   | Latest version using project ID | `P7dR8mSH`                                            |
   | Latest version of datapack      | `datapack:terralith`                                  |
   | Specific version of datapack    | `datapack:terralith:2.5.5`                            |
+  | Projects Listing File           | `@/path/to/modrinth-mods.txt`                         |
+
+!!! info "More about listing files"
+
+    Each line in the listing file is processed as one of the references above; however, blank lines and comments that start with `#` are ignored.
+    
+    Make sure to place the listing file in a mounted directory/volume or declare an appropriate mount for it.
+    
+    For example, `MODRINTH_PROJECTS` can be set to "@/extras/modrinth-mods.txt", assuming "/extras" has been added to `volumes` section, where the container file `/extras/modrinth-mods.txt` contains
+    
+    ```text
+    # This comment is ignored
+    fabric-api
+    
+    # This and previous blank line are ignore
+    cloth-config
+    datapack:terralith
+    ```
 
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