Use instance MR approval settings on compliance projects

What does this MR do?

This MR allows instance-level MR approval settings overrides on compliance projects.

The MR to allow recording the compliance framework scoping of these instance-level settings is done in !33923 (merged)

Relates to #219359 (closed)

Feature flag

This feature is under a feature flag: project_compliance_merge_request_approval_settings

Design notes

This MR adds flows highlighted in orange as below.

graph LR
  a[Project] --> b0{Licensed?}

  b0 -->|Enabled| b1{Feature flag?}
  b0 -->|Disabled| c1[Use project-level]

  b1 -->|Enabled| b{Compliance?}
  b1 -->|Disabled| c2(Existing behaviour)

  b -->|Yes| c{Regulated?}
  b -->|No| d[Use project-level]

  c -->|Yes| e[Use instance-level]
  c -->|No| f[Use project-level]

  classDef orange fill:#FDBC60;
  class b1,b,c,d,e,f orange;

Screenshots

Apply to framework

Instance Level	Project Level

Do not apply to framework

Instance Level	Project Level

Looking closely at the above screenshots:

1. When the compliance framework label (PCI-DSS) is selected on instance-level/ or the project is assigned the label, the instance-level MR approval settings will be the SSOT and the project-level control is disabled.
2. When the compliance framework label (PCI-DSS) is de-selected on instance-level/ or the project is unassigned the label, the project-level MR approval settings will be the SSOT and the project-level control is enabled.

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team