Exclude existing tiers/names from the protected environments creation form

Summary

There is a protected environment setting UI at project-level and group-level.

This issue is to ensure existing tiers/names are excluded from the protected environments creation form at group-level.

It should also resolve the following thread: !89599 (comment 981760671).

Problem

When you've selected a group that's allowed to deploy, it's not reflected in the Allowed to deploy dropdown within Protect an environment. If you try to re-select or add additional groups, you get an error.

Proposal

Remove environments from the Protect an environment dropdown that have already been protected, similar to protected branches (see screenshot below).