Invite members for tasks

What does this MR do and why?

The invite_members_for_tasks experiment was proven successful. This MR cleans up the experimentation code around the feature, thereby making it available for everyone.

Screenshots or screen recordings

See MR introducing this experiment.

How to set up and validate locally

See MR introducing this experiment.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.