Replace the 'Coding style proposal' issue template with a MR template

Signed-off-by: Rémy Coutable <remy@rymai.me>

.gitlab/issue_templates/Coding style proposal.md

-## Description of the proposal
-
-<!--
-Please describe the proposal and add a link to the source (for example, http://www.betterspecs.org/).
--->
-
-- [ ] Mention the proposal in the next backend weekly call and the #backend channel to encourage contribution
-- [ ] Proceed with the proposal once 50% of the maintainers have weighed in, and 80% of their votes are :+1:
-- [ ] Once approved, mention it again in the next backend weekly call and the #backend channel
-
-
-/label ~"development guidelines"
-/label ~"Style decision"
-/label ~documentation
-
-/cc @gitlab-org/maintainers/rails-backend

.gitlab/merge_request_templates/New static analysis check.md

+## Description of the proposal
+
+<!--
+Please describe the proposal and add a link to the source (for example, http://www.betterspecs.org/).
+-->
+
+### Check-list
+
+- [ ] Make sure this MR enables a static analysis check rule for new usage but
+  ignores current offenses
+- [ ] Create a follow-up issue to fix the current offenses as a separate iteration: ISSUE_LINK
+- [ ] Mention this proposal in the relevant Slack channels (e.g. `#development`, `#backend`, `#frontend`)
+- [ ] If there is a choice to make between two potential styles, set up an emoji vote in the MR:
+  - CHOICE_A: :a:
+  - CHOICE_B: :b:
+  - Vote yourself for both choices so that people know these are the choices
+- [ ] The MR doesn't have significant objections, and is getting a majority of :+1: vs :-1: (remember that [we don't need to reach a consensus](https://about.gitlab.com/handbook/values/#collaboration-is-not-consensus))
+- [ ] (If applicable) One style is getting a majority of vote (compared to the other choice)
+- [ ] (If applicable) Update the MR with the chosen style
+- [ ] Follow the [review process](https://docs.gitlab.com/ee/development/code_review.html) as usual
+- [ ] Once approved and merged by a maintainer, mention it again:
+  - [ ] In the relevant Slack channels (e.g. `#development`, `#backend`, `#frontend`)
+  - [ ] (Optional depending on the impact of the change) In the Engineering Week in Review
+
+/label ~"Engineering Productivity" ~"Style decision" ~"development guidelines" ~"static analysis"
+
+/cc @gitlab-org/maintainers/rails-backend