Add release tag GB when preparing the release PR

[jhnstn]

In the current release flow we add the release tag to GB after reviewing the PR.
In most cases we shouldn't need to wait for the review to add the tag since we rarely make changes to the GB pr once it's ready to review.

We can add some other flows to move the tag if needed and have the release publish (see #172) command verify that the tag is pointing to the last commit in the release pr