Create separate reactor POM to perform releases

Releases are currently performed from the root reactor POM. This triggers the execution of the release:prepare and release:perform goals on every module referenced from the reactor.

This approach prevents the individual release of some sub-modules. To enable individual releases, the least disruptive approach would be the creation of another reactor POM to reference every module in Oak that needs to be released in one big bulk. In example, oak-release/pom.xml or something along these lines.

The current reactor POM will remain untouched and will still reference every module in the project. This way, we will not have to change configuration of CI jobs out there.