Override ci.skip option when Pipeline execution policies are present

What does this MR do and why?

This change enforces pipeline to run if there are Pipeline execution policies applicable to the project regardless of ci.skip option.

Addresses suggestion from !150156 (comment 1931434533).

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

1. Enable the feature flag echo "Feature.enable(:pipeline_execution_policy_type)" | rails c
2. Create two new projects. One for testing and one as the security policy project
3. In the testing project, select Security & Compliance and Policies
4. Select Edit policy project
5. Select your security policy project and Save
6. On you security policy project, create a new file .gitlab/security-policies/policy.yml with content:

   ---
   pipeline_execution_policy:
   - name: Test
     description: ''
     enabled: true
     content:
       policy build:
         stage: build
         script:
         - echo "Policy build."
       policy test:
         stage: test
         script:
         - echo "Policy test."

7. Go to the testing project and create default .gitlab-ci.yml CI configuration.
8. Update README and commit the change with message [ci-skip] Update README
9. Verify that pipeline is running and includes the policy jobs.

Related to #464562 (closed)