#4664 Release pipeline (github actions)

[planetf1]

Signed-off-by: Nigel Jones nigel.l.jones+git@gmail.com

Partially implements #4664 (follows for snapshots, windows merge)

• Implements a simple, but sufficient (?) release pipeline in GitHub Actions
  • Requires repo owner to have setup an appropriate GPG key, distributed key, as secrets, and have permission to
    write to our project on maven central
  • Assumes required release testing are done before initiating the release
  • Builds using Java 8, maven
  • Initiated via creating a 'github release' OR by manually executing the workflow (for testing)
  • After execution maven central repo is left open for manual checking. Can then be 'close'-d to verify, and 'release'-d
    when ready. These steps are intentionally not automated

Merge pipeline to follow in subsequent PR

Also adds support for github repo in pom for future use