This adds land time checks before we try to merge. What this does is:
1. Merge changes into latest master, check out a new branch, push, and have a workflow that runs jobs from trunk (and maybe pull)
2. Wait for all checks in the landtime workflow to finish by using the GH API (graphql doesn't have this method from what I can see)
3. push the changes in

Test Plan:
Tested this in canary with a new workflow that passes and lint, tested what happens if i break the new workflow by exiting with 1, the normal flow, and some other flows.

Tested it breaking when land checks fail:
https://github.com/pytorch/pytorch-canary/pull/113#issuecomment-1165941716

Test that it works:
https://github.com/pytorch/pytorch-canary/pull/114#issuecomment-1165922791

Test that normal validations like PR is broken:
https://github.com/pytorch/pytorch-canary/pull/113#issuecomment-1165930037

Test that normal merge works:
https://github.com/pytorch/pytorch-canary/pull/113#issuecomment-1166751288

Test that force merge works:
https://github.com/pytorch/pytorch-canary/pull/113#issuecomment-1167507356
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77943
Approved by: https://github.com/janeyx99