Automate releases from OSSRH to Maven Central

[Ndiritu]

• Adds the Gradle Nexus Publish Plugin which allows closing and releasing from Nexus to Maven Central.
• Unfortunately it doesn't support dropping staging repositories. We also cannot download packages from staging repositories. This PR adds validation checks to ensure certain files are part of the package contents to be uploaded. The JARs are first published to the local maven cache & file contents inspected.
• For the prod release, we are only closing the staging repository using closeSonatypeStagingRepository. This will allow us to inspect the staging repository manually after these changes before we can switch to closeAndReleaseSonatypeStagingRepository with confidence that the automation works as expected.

part of #1257

[baywet]

LGTM besides a question

[github-actions]

Conflicts have been resolved. A maintainer will take a look shortly.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud