[MNG-8685] Propagate GitHub Actions debug mode to Maven

[ledoyen]

When in debug mode, GitHub Actions adds the RUNNER_DEBUG environment variable, cf https://github.com/actions/toolkit/blob/1b1e81526b802d1d641911393281c2fb45ed5f11/packages/core/src/core.ts#L258-L260.

It would be a great improvement for scoped troubleshooting to propagate this option to Maven. The use case is the following:

• A GitHub Actions workflow fails on a call to mvn
• We relaunch the failed jobs with the debug mode enabled
• Maven also displays its debug logs this time 🎉

It felt like such a minor change could avoid a new Jira entry, however I still can create one if you think it's best.

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https://issues.apache.org/jira/browse/MNG-8685

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[slawekjaranowski]

Idea is ok, but I would like to implement as possibility to execute

mvn ... --verbose=$ENV_NAME

I would like not add vendor specific name to code

eg, jenkins can have another values

It also will have a impact on out integration tests ....

[pzygielo]

I would like not add vendor specific name to code

Couldn't agree more!

[cstamas]

Agreed, there is ther place in core as well:
https://github.com/apache/maven/blob/master/impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/LookupInvoker.java#L938-L941

Maybe we want to pull these out into something like "CIDetector" helpers?

[cstamas]

I would like not add vendor specific name to code

Am fine with doing that, but having those encapsulated in some (helper) classes, like Jenkins, GH, etc.... The trick of this PR would be to not have to alter mvn invocation, like we use both: Jenkins and GH, and mvn could really "react" to both.

[cstamas]

My alt proposal: #2254