Create branches and tags for the voltha-2.12-beta branch

We cannot use branch/tag name: voltha-2.12-beta for early branching due to a guarded condition in the system that a release branch can only be a 3-digit semantic version.

Yes we could over-ride this check but that may lead to chaos downstream (w/o checking first) if conditional logic determines release candidates simply by testing for version=x.y.z.

In the interim we will re-use branch/tag={voltha-2.12, 2.12.0, v2.12.0}.

Initial creation will be labeled as the beta branch.

Subsequent release will simply update the release branch pointers to the latest version.