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

- made formatting consistent between each template
- updated the directions around the base-browser rebase to better reflect how
  we *actually* do it with regards to only rarely needing to rebase base-browser
  seperately
- fixed a few typos and incorrect git cherry-pick examples
- moved signing and tagging to their own section in the rebase templates
- changed instances of 'origin' to 'upstream' to be consistent with github/gitlab documentation
- added firefox-android section and marked android-components and fenix sections as optional for esr102 only so we don't have to urently fix this once we swithc to esr115