fixup! Bug 41649: Create rebase and security backport gitlab issue templates

Merge Info

• Related Issues

• Backport Timeline

  • Immediate - patchsets for critical bug fixes or other major blocker (e.g. fixes for a 0-day exploit) OR patchsets with trivial changes which do not need testing (e.g. fixes for typos or fixes easily verified in a local developer build)
  • Next Minor Stable Release - patchset that needs to be verified in nightly before backport
  • Eventually - patchset that needs to be verified in alpha before backport
  • No Backport - patchset for the next major stable

• Upstream Merging

  • Merge to base-browser - typically for !fixups to patches in the base-browser branch, though sometimes new patches as well
    • NOTE: if your changeset includes patches to both base-browser and tor-browser please please make separate merge requests for each part

• Issue Tracking

  • Link resolved issues with appropriate Release Prep issue for changelog generation

Change Description

Updates the security backport and rebase templates:

• adds explicit MR+backport steps for Android security fix backports
• adds example entry for CVE sections
• adds patch re-order step/guide to alpha rebases
• add branch protection steps for base-browser and tor-browser rebases so we don't lose patches merged during the rebase

/cc @pierov @dan @henry @ma1 @boklm