fixup! Adding issue and merge request templates

- removed exta unneeded dashes
- updated Backporting section to better match our desired process
  going forward:
  - discourage requests for backport to stable
  - provide justification for backport request from list proposed at
    last Tor meeting
  - added 'consistency' justification for patches/changes which can be difficult to context switch between but don't affect the final build output
  - added explicit merge destination selection

.gitlab/merge_request_templates/default.md

@@ -2,22 +2,33 @@
 
 <!-- Bookkeeping information for release management -->
 
-- ### Related Issues
+### Related Issues
 - tor-browser#xxxxx
+- mullvad-browser#xxxxx
 - tor-browser-build#xxxxx
-  - etc
 
-- ### 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
+### Backporting
 
-- ### 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
+#### Timeline
+- [ ] **Immediate**: patchset needed as soon as possible
+- [ ] **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 (preferred)**: patchset for the next major stable
 
-- ### Issue Tracking
+#### (Optional) Justification
+- [ ] **Emergency security update**: patchset fixes CVEs, 0-days, etc
+- [ ] **Censorship event**: patchset enables censorship circumvention
+- [ ] **Critical bug-fix**: patchset fixes a bug in core-functionality
+- [ ] **Consistency**: patchset which would make development easier if it were in both the alpha and release branches; developer tools, build system changes, etc
+- [ ] **Sponsor required**: patchset required for sponsor
+- [ ] **Other**: please explain
+
+### Merging
+- [ ] Merge to `tor-browser` - `!fixups` to `tor-browser`-specific commits, new features, security backports
+- [ ] Merge to `base-browser` -`!fixups` to `base-browser`-specific commits, new features to be shared with `mullvad-browser`, and security backports
+  - **NOTE**: if your changeset includes patches to both `base-browser` and `tor-browser` please clearly label in the change description which commits should be cherry-picked to `base-browser` after merging
+
+### Issue Tracking
 - [ ] Link resolved issues with appropriate [Release Prep issue](https://gitlab.torproject.org/groups/tpo/applications/-/issues/?sort=updated_desc&state=opened&label_name%5B%5D=Release%20Prep&first_page_size=20) for changelog generation
 
 ## Change Description