Prepare maven release

[NiklasRentzCAU]

Not completely done yet, steps yet needed to do:

• create the txt-record on de.cau.cs.kieler and let it verify: https://issues.sonatype.org/browse/OSSRH-91441
• create and add a KIELER user on Sonatype (or use own account instead)
• verify to use the KIELER GPG key with a valid email (kieler@informatik... maybe?)
• test a manual staging release with all of the above secrets locally
• test an automatic staging release with all of the above secrets within GH Actions
• start a real release

[NiklasRentzCAU]

First release is done locally, test with script will be done in a next release.