Override [ci skip] for scan execution policies

Release notes

Problem to solve

Similar to the improvements we made in pipeline execution policies to override [ci skip] behavior, we should align scan execution policies to do the same. This aligns with our goals for ensuring security and compliance.

Proposal

• Similar to the improvements we made in pipeline execution policies to override [ci skip] behavior, we should align scan execution policies to do the same.
• As we have to avoid introducing a breaking change, based on !174191 (comment 2233601465), we should make this configurable (disabled by default) and align the approach with the configuration we're adding for pipeline execution policies: Allow users to configure skip ci behavior for p... (!173480 - merged)

Steps to reproduce

1. Create new Project (ensure that AudoDevops is disabled)
2. Add Scan Execution Policy (Secure -> Policies -> Add new)
3. Merge MR with the updated policy
4. Commit to the project with [skip ci] in the commit body
5. CI will not execute for that commit

Verification steps

Example policy YAML:

scan_execution_policy:
  - name: Secrets
    description: ''
    enabled: true
    rules:
      - type: pipeline
        branch_type: all
    actions:
      - scan: secret_detection
    skip_ci:
      allowed: false

Example policy YAML with allowlist:

scan_execution_policy:
  - name: Secrets
    description: ''
    enabled: true
    rules:
      - type: pipeline
        branch_type: all
    actions:
      - scan: secret_detection
    skip_ci:
      allowed: false
      allowlist:
        users:
          - id: 13904527

Intended users

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