Membership Lock does not propagate from parent group to sub-groups

Right now whenever we create a subgroup, share_with_group_lock is inherited from the parent (https://gitlab.com/gitlab-org/gitlab-ee/blob/master/app/models/namespace.rb#L51). However this is not the case for membership_lock.

This can cause some confusion since it is inconsistent behaviour.

Screenshots

• Parent group settings

• Sub-group settings

This can be easily fixed by replicating what we do with share_with_group_lock in https://gitlab.com/gitlab-org/gitlab-ee/blob/master/app/models/namespace.rb#L51

\cc @DouweM