Provide a mechanism for dumping schemas of all events (and transitively included classes)

[PawelLipski]

Related to #28.

This would be priceless for detecting (esp. inadvertent) changes in events for the given PR in CI pipeline.

Possibly one of the serializers (kryo? borer?) already provides this functionality - pls research.

If not, then let's consider a Scala compiler plugin again (it could even just extract Scala source code of events and transitively included classes from the codebase).

[MarconZet]

I have researched Kryo and Borer. Kryo does everything at runtime. As expected, it doesn't know anything about classes it will serialise. Borer also doesn't keep its information in a central place. It's impossible to collect all codecs with certainty.

[MarconZet]

@PawelLipski
Maybe instead of compiler plugin, sbt task would be more appropriate? Either way, I doubt we can do it with something else than the compiler plugin (or maybe custom compiler, like the one in checker-plugin/test?), as we at least need AST to traverse through (which can be achieved with ANTLR, but that would be too much of a hassle).

[PawelLipski]

Ok! Leaving the details (compiler plugin/sbt task) up to you... if none of the existing serializers provides an easy way to extract the schemas, let's then make the schema dumper completely independent from what serializer has been used (just as akka-serializability-checker is)