Cleaning up leftover runners for org/repo

[mihaelabalutoiu]

• This PR implements cleanup of the orphan runners for org/repo.
• I updated the PR with the following changes:
  • I replaced the log.Fatalf with panic to prevent the exit 1 from interrupting the defer statement.
  • I put graceful cleanup functions in a function called GracefulCleanup and deferred it first.
  • Make sure that the graceful cleanup functions are idempotent.
  • I also added two functions: (GhOrgRunnersCleanup and GhRepoRunnersCleanup) to forcefully delete the runners via GitHub API and deferred them after the GracefulCleanup function.