Add support for expansions other than in module.properties

[thijslemmens]

@bhagyas poked me on the Alfresco discord about expansions in xml files inside the config directory in an amp. He found a workaround, but we should probably enable a more elegant way to do that.

[bhagyas]

(With Gradle 5.6, I used my fork of the SDK project.)
I used the following:

/**
 * Replaces tokens in xml files.
 */
task replaceTokens(type: Copy) {
  from("src/main/amp/config") {
    include '**/*.xml'

    //ignore context and patches
    exclude '**/context/*'
    exclude '**/patches/*'

    //replace version property
    expand('version': version)
  }
  into tokenReplacedDir
  sourceSets.main.amp.config.srcDirs += tokenReplacedDir
}

whereas tokenReplacedDir was declared as $buildDir/replaced-files