Resolves s4u/maven-settings-action#348, plugin repositories support

[pwoodworth]

Add support for pluginRepositories as per issue #348

A configuration like the following:

steps:
- uses: s4u/maven-settings-action@master
  with:
    pluginRepositories: >-
      [{
        "id": "repoId",
        "name": "repoName",
        "url": "url",
        "releases": {
          "enabled": false
        },
        "snapshots": {
          "enabled": true
        }
      }]

Will result in a settings.xml like the following:

<profiles>
  <profile>
    <id>_custom_repositories_</id>
    <activation>
        <activeByDefault>true</activeByDefault>
    </activation>
    <repositories/>
    <pluginRepositories> 
      <pluginRepository>
        <id>repoId</id>
        <name>repoName</name>
        <url>url</url>
        <releases><enabled>false</enabled></releases>
        <snapshots><enabled>true</enabled></snapshots>
      </pluginRepository>
    </pluginRepositories>
  </profile>
</profiles>

[slawekjaranowski]

@pwoodworth thanks