Support Markdown for Feature Flags

Release notes

In this release we have added markdown support for feature flags. Users can mention [feature_flag:<IID>] in discussions or comments to refer a specific feature flag. Clicking on the generated link, will jump to the feature flag's edit page. This makes collaboration on feature flags much easier and more convenient.

https://docs.gitlab.com/ee/user/markdown.html

Problem to solve

A user wants to reference feature flags from discussions in GitLab

Proposal

Implemented in !53021 (merged)

A user can use [feature_flag:] to reference the feature flag that is not supported by markdown

This can be used for referencing in MRs/issues/epics and in discussions

Not supported in GitLab Core is the ability to link feature flags to issues.