Generic rules for build users

[jjohannes]

Even if this plugin is used, sometimes users need to add their own rules. In certain cases, there is not the "one truth", but it depends on the usage context which things you want/need to adjust in the metadata for a library. This is clunky with vanilla Gradle if you want the rules to be @CacheableRule, as you need to create a separate class for each rule, instead of a "one-liner" in the build script.

If we are in Java/JVM projects, there are certain patterns for rules you usually need. This plugin could provide a parameterisable rule for each of these:

1. Add a capability (to all variants)
2. Add dependencies (to all variants)
3. Remove dependencies (from all variants)
4. Make a feature known (classifier Jar exists, but is not in the metadata)
5. Add alignment constraints to all components of a library (related Alignment rules #22)
6. Add native variants (libraries that publish multiple Jars for different target platforms - like Component rule for JavaFX components #57)