[Feature flag] Rollout of `group_level_release_statistics`

What

Remove the :group_level_release_statistics feature flag.

Owners

• Team: ~"group::release"
• Most appropriate slack channel to reach out to: #s_release
• Best individual to reach out to: @nfriend

Expectations

What are we expecting to happen?

Two new fields - releasesCount and releasesPercentage - will be made available in the GraphQL endpoint.

What might happen if this goes wrong?

The queries behind these fields are relatively complex and have the potential to cause performance issues if queried heavily.

Roll Out Steps

• Remove feature flag

Rollback Steps

• This feature can be disabled by running the following Chatops command:

/chatops run feature set --project=gitlab-org/gitlab group_level_release_statistics false