Allow user to show only protected branches when filtering the view from the `/branches` UI
### Problem to solve
As a non-administrator, I want to see the summary of all protected branches
Because those represent "official" releases or sanctioned branch-points (we use tags as well, but branches as another mechanism)
From the `branches/` view in the UI, you can't filter to protected branches. I see the "protected" "badge" on `master`, for example, but I'm curious what other branches are protected
### Proposal
Either:
1. A new tab alongside `Active` `Stale` `All`
2. Support the query `is:protected` (or similar)

### What does success look like, and how can we measure that?
Fewer questions from non-administrators to adminstrators about what branches are protected
Fewer clicks for anyone who's curious
People tend to use protected branches more often
People clamor more frequently to administrate from the `branches/` UI which branches are protected :stuck\_out\_tongue\_winking\_eye:
issue