Configure advanced GitHub Actions workflows

[rdeltour]

We've started using GitHub Actions for automated builds (see #1261).

Check list:

• [x] Setup a CI workflow #1263
  • [x] run simple Maven verify build
  • [x] cache Maven dependencies
  • [x] setup a build matrix equivalent to what we had in Travis
  • [x] add a build badge on the Readme page
  • [x] push Maven snapshots on successful builds of the main branch
• [ ] Setup a release build?
  • [ ] generate the change log
  • [ ] update the readme
  • [ ] create git tag
  • [ ] publish artifacts to OSSRH
  • [ ] create release
    • [ ] get release notes from template + change log
    • [ ] attach the previously-built artifact