Consider lowering minimal required Maven version

In #355 (closed) we configured Maven 3.8.1 as minimal required Maven version for our Maven build. This then matches the embedded Maven version of the Eclipse 2021-06 release that we use, and the version of Maven configured in our Jenkinsfile. This should not be a problem for our build launch configurations within our development environment.

However, when running Maven from the command line outside Eclipse, and using older Linux distributions with system package managers that don't provide this Maven version, this may pose issues. See e.g. !303 (comment 694809).

As such, maybe we should configure the minimal Maven version to the real minimum version that is required to successfully run our build.

So what is the minimal Maven version then?

• The release notes of Tycho 2.0 indicate Maven 3.6.3 is the minimal required version for that Tycho release.
• The release notes of Tycho 2.1 don't indicate a Maven version.
• The release notes of Tycho 2.2 to 2.7.1 also don't indicate a change in Maven version requirements.

I thus think we could lower the minimal Maven version requirement from 3.8.1 to 3.6.3.