Branch renaming and protection

[anEXPer]

I'm opening and then very shortly closing this issue to document a couple of things that I've just done.

One, I've enabled branch protection, requiring PRs and at least two reviewers.

Two, I've renamed the master branch release to align with the broader git ecosystem's deprecation of master as default branch name.

I've done this to gain experience with these settings and changes, as broader VMware policy expects both things, and this is a relatively low-risk repo on which to start rolling these changes out across the TAS-ecosystem repos in the pivotal org.

One or both of these may cause automation breakage, or provoke the need for followup actions; if you need help, make an issue and tag me, I'll sort it out.