Add `ref_protected` to branch and tag webhooks

What does this MR do and why?

Make it possible to determine whether the given ref was protected at the time of webhook generation, s.t. webhook integrators can operate on this data in a similar fashion to JWT consumers within builds.

Includes changelog tag added and API documentation updates.

Note: This is my first GitLab contribution, apologies in advance if I misstep on the process!

Screenshots or screen recordings

None, but I'd gladly accept help proving this has the desired impact. It did not seem trivial to validate by hand.

How to set up and validate locally

1. Set up a webhook integration w/ the test instance
2. Generate a push and/or tag webhook via normal means (git operations)
3. Observe the newly added fields are present and correctly populated

MR acceptance checklist

• I have evaluated the MR acceptance checklist for this MR.