RFC: New transformers

[snazy]

@Goooler I've created a couple new transformers. Would you mind taking a look which ones you think make sense for the project? I would then create individual PRs including tests for each of those.

• Deduplicating transformer - to include the same path for the same content only once, detects conflicts
• Merge property files transformer - to merge the properties of property files with the same path, detecting conflicts
• Merge license files transformer - to produce a license with with the project's license and the license files from the dependencies (but yea, no info about the actual Maven GAV)
• Enhance the Apache Notice transformer to make the output-path and source file patterns configurable
• Tool/convenience task to find dependencies that contain a matching pattern-filterable to debug conflicts.
• Helper class for the above task + transformers (hide boilerplate code)

[snazy]

(Just maintaining the branch for this draft PR as a "collection of things to split out".)