Add a new feature flag remove_non_gma_memberships

What does this MR do?

Add a new feature flag remove_non_gma_memberships, this feature flag is to allow the release of GMAs without including the side of effects or removing other groups or project memberships while converting accounts to GMAs, which could be disruptive.

Does this MR meet the acceptance criteria?

Conformity

Closes #211374 (closed)

Edited by Sebastián Arcila Valenzuela