Add metrics for pipeline execution policy usage

What does this MR do and why?

Add metrics for pipeline execution policy usage

Related to: #436055 (closed)

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.

Screenshots or screen recordings

How to set up and validate locally

1. Enable the pipeline_execution_policy_type feature flag

Feature.enable(:pipeline_execution_policy_type)

2. Create a new group
3. Go to Settings > General > Permissions and group features
4. Enable the Security policy pipeline execution action experiment
5. Create a new project
6. Add a .gitlab-ci.yml with the content

test:
  stage: test
  script:
    - echo "Do a test here"

7. Go back the group

8. Create a new project

9. Go to Secure > Policies

10. Click in New policy

11. Select Pipeline execution policy

12. Create a new policy injecting the content from the .gitlab-ci.yml

13. Click in update via merge request

14. Start the event monitoring running the command bellow in the gdk-folder/gitlab directory

rails runner scripts/internal_events/monitor.rb enforce_pipeline_execution_policy_in_project

15. Go to Build > Pipelines and run a pipeline
16. Check if the counter was increased in the event monitoring.