Execute Sonar analysis with GHA (including code coverage)

[kwin]

As the idea is to drop the Eclipse Jenkins (https://ci.eclipse.org/sisu/) altogether we should solely rely on GitHub Actions for building. The should comprise Sonarcloud as well (as outlined in https://docs.sonarsource.com/sonarcloud/advanced-setup/ci-based-analysis/sonarscanner-for-maven/) as the regular analysis being executed on Solarcloud.io never calculates any coverage information (https://docs.sonarsource.com/sonarcloud/enriching/test-coverage/overview/).

We already have a matrix build in place. The idea is to execute the Sonar Maven plugin only once (with JDK17 or newer) on a single OS.

Prerequisites:

• Sonarcloud Token available as GH secret (requested in https://gitlab.eclipse.org/eclipsefdn/helpdesk/-/issues/4700)