Merge branch 'doc-add-experiment-cleanup-issue-template' into 'master'

Add successful experiment cleanup template

See merge request !48259

.gitlab/issue_templates/Experiment Successful Cleanup.md

+<!-- Title suggestion: [Experiment Name] Successful Cleanup -->
+
+## Summary
+
+The experiment is currently rolled out to 100% of users and has been deemed a success.
+The changes need to become an official part of the product.
+
+## Steps
+
+- [ ] Determine whether the feature should apply to SaaS and/or self-managed
+- [ ] Determine whether the feature should apply to EE - and which tiers - and/or Core
+- [ ] Determine if tracking should be kept as is, removed, or modified.
+- [ ] Migrate experiment to a default enabled [feature flag](https://docs.gitlab.com/ee/development/feature_flags/development.html) for one milestone and add a changelog. Converting to a feature flag can be skipped at the ICs discretion if risk is deemed low with consideration to both SaaS and (if applicable) self managed.
+- [ ] Ensure any relevant documentation has been updated.
+- [ ] In the next milestone, [remove the feature flag](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up).
+- [ ] After the flag removal is deployed, [clean up the feature/experiment feature flags](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up) by running chatops command in `#production` channel
+
+/label ~"feature" ~"feature::maintenance" ~"workflow::scheduling" ~"growth experiment" ~"feature flag"