Merge branch 'retro-13.3-followup-template' into 'master'

Issue Template for implementation issues

Closes gitlab-org/threat-management/general#737

See merge request gitlab-org/gitlab!42427

.gitlab/issue_templates/Implementation.md

+<!--
+Implementation issues are used break-up a large piece of work into small, discrete tasks that can
+move independently through the build workflow steps. They're typically used to populate a Feature
+Epic. Once created, an implementation issue is usually refined in order to populate and review the
+implementation plan and weight.
+Example workflow: https://about.gitlab.com/handbook/engineering/development/threat-management/planning/diagram.html#plan
+-->
+
+## Why are we doing this work
+<!--
+A brief explanation of the why, not the what or how. Assume the reader doesn't know the
+background and won't have time to dig-up information from comment threads.
+-->
+
+
+## Relevant links
+<!--
+Information that the developer might need to refer to when implementing the issue.
+
+- [Design Issue](https://gitlab.com/gitlab-org/gitlab/-/issues/<id>)
+  - [Design 1](https://gitlab.com/gitlab-org/gitlab/-/issues/<id>/designs/<image>.png)
+  - [Design 2](https://gitlab.com/gitlab-org/gitlab/-/issues/<id>/designs/<image>.png)
+- [Similar implementation](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/<id>)
+-->
+
+
+## Non-functional requirements
+<!--
+Add details for required items and delete others.
+-->
+
+- [ ] Documentation:
+- [ ] Feature flag:
+- [ ] Performance:
+- [ ] Testing:
+
+
+## Implementation plan
+<!--
+Steps and the parts of the code that will need to get updated. The plan can also
+call-out responsibilities for other team members or teams.
+-->
+
+- [ ] ~frontend Step 1
+  - [ ] @person Step 1a
+- [ ] ~frontend Step 2
+
+
+<!--
+Workflow and other relevant labels
+
+~"group::" ~"Category:" ~"GitLab Ultimate"
+-->
+/label ~"workflow::refinement"
+
+<!--
+Other settings you might want to include when creating the issue.
+
+/milestone %"Next 1-3 releases"
+/assign @
+/epic &
+-->