Add a .mvn/maven.config that contains the maven arguments shared in the
Jenkins-CI, GitHub workflow and for a local build.
This also enables the 'build-individual-bundles' profile for all of the
mentioned scenarios, so that one does not have to specify it manually
anymore.

The property 'project.build.sourceEncoding=UTF-8' is already defined in
the 'eclipse-platform-parent' pom and is therefore unnecessary.

In the Jenkins build additionally define the
properties'maven.test.error.ignore=true' and
'maven.test.failure.ignore=true' in order to only mark the build as
unstable if there are test-failures/errors so that it is simpler to
distinguish from other failures in the build.