[MPLUGINTESTING-93] Documentation for Plugin testing

[aamotharald]

Added Docu on how to test with JUnit5.
Converted the Docu from apt to md .
This PR should only get merged once org.apache.maven.plugin-testing:maven-plugin-testing-harness:3.4.0 has been released as on 3.3.0 there is no JUnit5 testing support at all.

[Bukama]

Thanks for the migration. Got some comments, you may want to consider.

P.S. I personally prefer to write only one sentence per line in a documentation as code file, but I don't know if maven has clear rules about this.

[aamotharald]

Thanks @slawekjaranowski @elharo and @Bukama for your review! I learned a lot and was able to address your review comments with (for me) sound solutions.

[elharo]

delete "to support the legacy @Component annotation."

I've eliminated all of those

[Bukama]

Can't add anything to what @elharo has already mentioned.

[elharo]

delete "(an open-source software framework for the Java platform)" as it doesn't add much. Folks can Google it if they've never heard of it

[elharo]

and might as wellm delete "(a collection of components used by Apache Maven)" too

[slawekjaranowski]

Thanks for work ... By the way I would like to have such documentation in project in branch 3.x
https://github.com/apache/maven-plugin-testing/tree/maven-plugin-testing-3.x

I'm still think that release of 3.4.0 - maven-plugin-testing should be done ... on my list 😄

[Bukama]

@aamotharald Sorry for the long time not responding. We are still interested in the changes of your PR. Would you refresh it (put in last comments and resolve conflicts) :)

[slawekjaranowski]

@aamotharald thanks for the effort, we have done similar updates in:

• Add unit test example with mocking for plugin #1435
• Update example for maven-plugin-testing #1437

so I close it