Add Maven plugin repository support

Generate plugin repositories alongside dependency repositories and share Central inclusion and ordering controls. Cover repository parsing, credentials, explicit Central overrides, plugin ordering, and effective Maven models; document the compatibility change and rebuild runtime bundles.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 52a8a8e2-7965-42d3-88d9-d66f64d0d60d

docs/advanced-usage.md

@@ -1003,14 +1003,92 @@ This configuration adds the following active profile to `settings.xml`:
 </activeProfiles>
 ```
 
-Maven Central is included first by default. Set
-`mvn-repositories-prioritize-central: false` to place custom repositories
-first, or set `mvn-repositories-include-central: false` to disable Central. The
-generated profile overrides the Central repository inherited from Maven's Super
-POM with releases and snapshots disabled. When automatic Central inclusion is
-off, the ID `central` may instead be declared explicitly in `mvn-repositories`
-to replace it with a user-specified repository; otherwise that ID is reserved
-to prevent duplicate entries.
+Maven Central is included first by default. The Central controls apply to both
+dependency and plugin repositories. Set
+`mvn-repositories-prioritize-central: false` to place custom repositories first
+within each configured list, or set `mvn-repositories-include-central: false` to
+disable Central for both types. The generated profile overrides the dependency
+and plugin Central repositories inherited from Maven's Super POM with releases
+and snapshots disabled, even if only one custom repository list is supplied.
+These controls have no effect when neither list contains a nonblank entry.
+
+When automatic Central inclusion is off, the ID `central` may instead be
+declared explicitly in `mvn-repositories` or `mvn-plugin-repositories` to replace
+it with a user-specified repository for that type. Declaring it in one list
+does not enable Central in the other. Otherwise that ID is reserved to prevent
+duplicate entries. Other repositories declared in your project's POM are not
+disabled by these controls.
+
+### Resolving Maven plugins from custom repositories
+
+Maven resolves build plugins through `<pluginRepositories>`, separately from
+dependency `<repositories>`. Use `mvn-plugin-repositories` to configure plugin
+resolution with the same multiline `repository-id:repository-url:snapshots-enabled`
+format. It can be supplied without `mvn-repositories`; dependency repositories
+are not automatically used as plugin repositories.
+
+For example, configure the same private repository for dependencies and plugins
+and disable inherited Maven Central for both:
+
+```yaml
+steps:
+  - uses: actions/checkout@v7
+  - uses: actions/setup-java@v6
+    with:
+      distribution: 'temurin'
+      java-version: '21'
+      mvn-server-credentials: |
+        private:PRIVATE_REPOSITORY_USERNAME:PRIVATE_REPOSITORY_TOKEN
+      mvn-repositories: |
+        private:https://maven.example.com/releases:false
+      mvn-plugin-repositories: |
+        private:https://maven.example.com/releases:false
+      mvn-repositories-include-central: false
+  - run: mvn --batch-mode verify
+    env:
+      PRIVATE_REPOSITORY_USERNAME: ${{ secrets.PRIVATE_REPOSITORY_USERNAME }}
+      PRIVATE_REPOSITORY_TOKEN: ${{ secrets.PRIVATE_REPOSITORY_TOKEN }}
+```
+
+The matching ID `private` selects the same server credentials for both types.
+IDs must be unique within each list, but can be shared across the two lists.
+Public repositories do not require a matching credential entry.
+
+Alongside dependency repositories, the active `setup-java-repositories` profile
+contains:
+
+```xml
+<pluginRepositories>
+  <pluginRepository>
+    <id>private</id>
+    <url>https://maven.example.com/releases</url>
+    <snapshots>
+      <enabled>false</enabled>
+    </snapshots>
+  </pluginRepository>
+  <pluginRepository>
+    <id>central</id>
+    <url>https://repo.maven.apache.org/maven2</url>
+    <releases>
+      <enabled>false</enabled>
+    </releases>
+    <snapshots>
+      <enabled>false</enabled>
+    </snapshots>
+  </pluginRepository>
+</pluginRepositories>
+```
+
+Omitting a Central override would leave the Super POM's plugin repository
+enabled. In particular, `mvn-repositories-include-central: false` now disables
+inherited plugin Central even for existing workflows that only configure
+`mvn-repositories`. To download plugins in such workflows, configure a plugin
+repository or explicitly declare `central` in `mvn-plugin-repositories`.
+
+With Central included, it is placed before custom plugin repositories by
+default; `mvn-repositories-prioritize-central: false` places it after them.
+All repository generation respects `settings-path` and `overwrite-settings`;
+an existing settings file is left untouched when `overwrite-settings: false`.
 
 ### GPG