dependencyUpdates for example projects

[Jolanrensen]

Helps #1661

Adapts dfbuild.dependencyUpdates convention plugin:

• Makes versionsToSync type safe
  • (Note, we always need to format versions with -, but we already do this)
• Added every missing dependency from our examples in the main gradle/libs.versions.toml
• Created exampleDependencyUpdates configuration that consumes every dependency from our examples, so the dependencyUpdate task is aware of them.
  • (I would have liked this to be automatic, but I cannot find a way to do that in a transparent manner, unfortunately...)
  • (If you know a better way, or if I missed a dependency, please let me know!)

As you can see, running dependencyUpdates now also detects out-of-date android dependencies :D