switch to official Antora Plugin for Gradle

- lock version to latest release of Antora 3.1
- declare Node.js dependencies in build.gradle
- use Node.js version provided by plugin
- assign environment variables using environments property on extension block
- move group and description project properties to gradle.properties
- remove unneeded .npmrc
- upgrade to Gradle 7.5.1
- pass -q when running gradlew from Collector

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.4.2-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-7.5.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists