Improve correctness/completeness of Feature Flags data

We started scraping Feature Flags YAML for the analytics purposes, but data need more help with:

• not all of them have group assigned, we would have to go and manually assign these 46 flags
• not all of them have milestone assigned, we would have to do it manually for these 60 flags
• some of them have wrong groups as you can see, we can correct them and they will be updated on next update
• it would help to sanitise groups used, maybe add a Danger extension to ensure that group is exactly the same as one assigned via label for MR: groupmemory
• all of the above needs to be done updating YAML files with a text editor: https://gitlab.com/gitlab-org/gitlab/-/tree/master/config/feature_flags/development and https://gitlab.com/gitlab-org/gitlab/-/tree/master/ee/config/feature_flags/development

I think thats all. These data for type: :development are always kept accurate on additions and removals (sometimes creating master:broken due to that: #284596 (closed)).