[Feature flag] Rollout of `personal_snippet_reference_filters`
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## What
Remove the `:personal_snippet_reference_filters` feature flag ...
## Owners
- Team: Create::Editor
- Most appropriate slack channel to reach out to: `#g_create_editor`
- Best individual to reach out to: `@vij` or `@fran`
## Expectations
### What are we expecting to happen?
References to resources added to `PersonalSnippet` comments and descriptions should be converted via the GFM/AbstractReferenceFilter to GitLab references ([docs](https://docs.gitlab.com/ee/user/markdown.html#special-gitlab-references)) on create/update and preview of changes.
### What might happen if this goes wrong?
References may not be generated correctly
### What can we monitor to detect problems with this?
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## Beta groups/projects/users
We can beta test by enabling for individual users, e.g. vij or fjsanpedro
## Roll Out Steps
- [ ] Enable on staging
- [ ] Test on staging
- [ ] Ensure that documentation has been updated
- [ ] Enable on GitLab.com for individual users listed above and verify behaviour
- [ ] Coordinate a time to enable the flag with `#production` and `#g_delivery` on slack.
- [ ] Announce on the issue an estimated time this will be enabled on GitLab.com
- [ ] Enable on GitLab.com by running chatops command in `#production`
- [ ] Cross post chatops slack command to `#support_gitlab-com` ([more guidance when this is necessary in the dev docs](https://docs.gitlab.com/ee/development/feature_flags/controls.html#where-to-run-commands)) and in your team channel
- [ ] Announce on the issue that the flag has been enabled
- [ ] Remove feature flag and add changelog entry
- [ ] After the flag removal is deployed, [clean up the feature flag](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up) by running chatops command in `#production` channel
issue