Add suffix configuration option to Pipeline execution policies

What does this MR do and why?

Uniqueness enforcement causes challenges for compliance teams that may use the built-in templates twice, causing the jobs to be duplicate.

With this change we are adding a new policy configuration option suffix: on_conflict/never. The default value is on_conflict.

If policy uses suffix: on_conflict and a job with the same name exists in the pipeline, we will add suffix in a format :policy-<security-policy-project-id>-<policy-index>.

The suffix is added following the policy hierarchy.

MR acceptance checklist

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Before (or with FF disabled)	After

Dependency on a conflicting job	Dependency on a non-conflicting job	Dependencies on both jobs

How to set up and validate locally

1. Enable feature flag pipeline_execution_policy_suffix.
2. Create a project
3. Create .gitlab-ci.yml:

   include:
     - template: Jobs/Secret-Detection.gitlab-ci.yml
   
   duplicate-job:
     stage: test
     script:
       - echo "From project."

4. Create pipeline execution policy with suffix: on_conflict (or without this option specified) and the following config file:

   include:
     - template: Jobs/Secret-Detection.gitlab-ci.yml
   
   duplicate-job:
     stage: test
     script:
       - echo "From policy."

5. Run a pipeline and verify that there is no error
6. Verify that duplicate-job:policy-<spp-id>-<policy-index> is added into the pipeline in addition to the duplicate-job and its output says "From policy."
7. Update the policy CI file to add more jobs and define dependencies:

   other-policy-job:
     script:
       - "sleep 60 && echo 'policy'"
   
   rspec:
     stage: .pipeline-policy-pre
     script:
       - "sleep 20 && echo 'rspec'"
   
   jest:
     stage: test
     script:
       - "sleep 10 && echo 'jest'"
   
   upload-rspec-coverage:
     stage: deploy
     needs:
       - rspec
     script:
       - echo "requires rspec"
   
   upload-jest-coverage:
     stage: deploy
     needs:
       - jest
     script:
       - echo "requires jest"
   
   deploy:
     stage: deploy
     needs:
       - rspec
       - jest
     script:
       - echo "deploy"

8. Update project's .gitlab-ci.yml to also define rspec job:

   project-job:
     script:
       - echo "project"
   
   rspec:
     script:
       - echo "project rspec"

9. Run a pipeline and verify that dependencies were updated correctly for the suffixed job
10. Change the policy to suffix: never and verify that a job uniqueness error is raised when you try to run a pipeline.

Related to #473189 (closed).