Set an approval rule to deployment approval

What does this MR do and why?

This MR adds the Internal logic for Multi Access Levels in Deployment Approval.

• Extend Deployments::ApprovalService (The SSOT service that users can approve/reject deployment) to set ProtectedEnvironments::ApprovalRule to Deployments::Approval.
• Delete both ProtectedEnvironments::DeployAccessLevel and ProtectedEnvironments::ApprovalRule when an assigned group/user has been removed from the protected environment.
• Add deployment_approval_rules feature flag to shut out the new logic until all MRs have been merged.

These internal logic will be used in an upcoming MR. Please see PoC MRs - PoC 1, PoC 2 for the overview.

A few notes:

• Previous MR is !82800 (merged).
• You can find more feature concept of Protected Environment in the documentation.

Screenshots or screen recordings

N/A (See the manual QA result of PoC)

How to set up and validate locally

N/A (See the manual QA result of PoC)

MR acceptance checklist

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