Scope save_issuable_health_status flag to group

What does this MR do?

save_issuable_health_status feature flag is scoped to project in some places, to groups in other places and not scoped at all on GraphQL.

This will cause problems when turning on the flag only for one group, since the results will be different for each place the flag is checked.

This makes all flags be scoped for groups and remove it from GraphQL since it does not accept any scopes.

For more information check the discussion: #209881 (comment 302481652).