[CI-IMPROVEMENT-9] Implement check-required workflow that checks if all required checks are successful and not skipped

[pavlovic-ivan]

What type of PR is this?

This is an improvement PR

What this PR does / why we need it:

9th in a series of PRs for improvements. This implements check-required workflow that verifies if all required checks are successful, which is the case with the job in the CI workflow.

Notes for maintainers

Prerequisites:

• Create a Github app that has permissions: "Read access to metadata" and "Read and write access to checks"
• Create an env create-check with a protection rule for master branch with two secrets APP_ID and APP_PRIVATE_KEY and copy the apps creds created in the previous step

After merging the PR

• update branch protection to enforce the required check to originate from the new GitHub app

Work based on these two PRs as a reference:

• Create "All required checks succeeded" check run when "All required checks done" CI job is actually successful G-Research/fasttrackml#241
• Improve required checks creation in CI G-Research/fasttrackml#458

FIxes: #3189

[dave-gantenbein]

Do we want to do any handling of cases where we're not completed successfully here?

[pavlovic-ivan]

This else block here is only informational. It's not necessary, but since the code is taken from FML, maybe they benefit from this info, which then makes this contribution identical to what they use. @jgiannuzzi what do you think of this? does FML benefit from it or not? should i remove it, so both are identical (making it easier to extract to separate repo later)

[jgiannuzzi]

@dave-gantenbein any other case is handled by newCheck's default status that is set to in_progress. Basically we only create our successful check when we have found a successful check, otherwise we mark it as pending.