Release pipeline should check existence of GA version

During the release of Alpha1, I had not setup 1.9.GA as a version in Jira and this caused the Set Target Release stage in the release pipeline to fail but the error was actually a 400 error indicating a bad request. After debugging the JSON response was:

{"errorMessages":[],"errors":{"customfield_12311240":"Version name '1.9.GA' is not valid"}}

So we should check for the GA version existence and raise a clear error if it doesn't exist.

We can adjust the findVersion() call so that its parameterized so we can re-use it for GA version checks as well.