Verify ci config for default and stable branches

What does this MR do and why?

Addresses #34040 (closed) iteration 1 and 5

This MR creates 2 manual jobs in Gitlab Pipeline when changes are made to the Gitlab CI.

• pipeline-config-test stable-branch
• pipeline-config-test default-branch

These jobs are allowed to fail, and must be manually triggered since they are resource intensive. The following actions will take place:

• a new Gitlab branch will be created (a test branch mimicing a stable branch or default branch, depending on the job)
• There will be a pipeline created for that branch.
• pipeline jobs will be validated against a reference pipeline(if User provides the reference pipeline ID through a REFERENCE_PIPELINE_ID environment variable), or it will compare against the list of jobs stored in expected_default_branch_jobs or expected_stable_branch_jobs to see if there are any job inconsistencies, either missing or added.
• the pipeline is cancelled right after the last step finishes, to avoid pipelines taking up too much resources
• the test branch gets deleted

What needs to be improved:

The jobs have the following 3 scripts:

create_branch "$TEST_BRANCH" "$CURRENT_COMMIT" "$GITLAB_RPOJECT_ID"
create_pipeline_and_validate_jobs "$PIPELINE_CONTEXT" "$TEST_BRANCH" "$GITLAB_RPOJECT_ID"
delete_branch "$TEST_BRANCH" "$GITLAB_RPOJECT_ID"

1. If the job failed during the 2nd script, we need to manually delete the branch created by script 1 before we can rerun the jobs.
2. The list of expected jobs is actually more than what would run in a regular stable or default branch, because the reference job list was generated from a branch that contains ci changes and therefore triggers more jobs than usual. I need to trim down the list of jobs so it doesn't include the ones that only run for CI changes.

Screenshots or screen recordings

Added these 2 manual jobs in the sync stage below:

Example of a matching test result: https://gitlab.com/gitlab-org/gitlab/-/jobs/3074374225

Example of a test showing that the pipeline jobs are inconsistent with the reference pipeline:

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.