Add fields to Branch Protection endpoint

[yardenshoham]

Fixes#2719

This adds a few fields that were requested in #2719.

[codecov]

Codecov Report

Merging #2744 (23e1c6e) into master (4fec23d) will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #2744 +/- ##
=======================================
Coverage 98.05% 98.05% =======================================
Files 132 132 Lines 11611 11611 =======================================
Hits 11385 11385 Misses 154 154 Partials 72 72 

Impacted Files	Coverage Δ
github/repos.go	98.84% <ø> (ø)

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[gmlewis]

Thank you, @yardenshoham.
Please correct the issues below and make sure to re-run gofmt and go generate ./... and push (not force-push since we always squash and merge PRs in this repo) the changes to this PR.

[yardenshoham]

Thanks, changes applied

[gmlewis]

Thank you, @yardenshoham !
LGTM.
Merging.