gitlab: create templates for bug reports and release MRs

.gitlab/issue_templates/Bug.md

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+<!--
+### Precheck
+
+* For support use https://git.pleroma.social/pleroma/pleroma-support or [community channels](https://git.pleroma.social/pleroma/pleroma#community-channels).
+* Please do a quick search to ensure no similar bug has been reported before. If the bug has not been addressed after 2 weeks, it's fine to bump it.
+* Try to ensure that the bug is actually related to the Pleroma backend. For example, if a bug happens in Pleroma-FE but not in Mastodon-FE or mobile clients, it's likely that the bug should be filed in [Pleroma-FE](https://git.pleroma.social/pleroma/pleroma-fe/issues/new) repository.
+-->
+
+### Environment
+
+* Installation type:
+  - [ ] OTP
+  - [ ] From source
+* Pleroma version (could be found in the "Version" tab of settings in Pleroma-FE): 
+* Elixir version (`elixir -v` for from source installations, N/A for OTP):
+* Operating system:
+* PostgreSQL version (`postgres -V`):
+
+
+### Bug description

.gitlab/merge_request_templates/Release.md

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+### Release checklist
+* [ ]  Bump version in `mix.exs`
+* [ ]  Compile a changelog
+* [ ]  Create an MR with an announcement to pleroma.social
+* [ ]  Tag the release