[OLD] Run tier tests on Testing Farm

[ansasaki]

Add a reusable workflow that schedule tests on testing farm using the CLI. If the specified plan is not found, the test is ignored and passes.

The tier tests are executed sequentially using the reusable workflow. The tests from the tier1.yaml plan are executed on a single distro, currently Fedora 37.

If the 'tier' input is set as 'tier2', the tests from the tier2.yaml plan are executed in multiple distros, currently Fedora 37 and 38.

To avoid the need for every contributor to have their own Testing Farm token, the following 2-step trick is implemented.

1. A workflow is triggered when a PR is opened. This workflow will not actually run the tests as the repository secrets are not accessible. It will only store the PR info as an artifact.
2. A workflow is triggered when the first workflow is completed. This will actually run the tests as it will have access to the secrets, but it will use the workflow code from the repository (i.e. code already merged). This means that PRs that changes workflows cannot be tested this way (will only be effective after merging). Since this second workflow is not tied with a PR (as it was triggered not by the "pull_request" event, but by the finish of the first workflow), the results of the tests will not be shown on the PR that originated the tests. To make that connection, we need to implement the "check" API from github, to show the test results on the PR.

[ansasaki]

To see what happens, I merged this PR in my own repo: https://github.com/ansasaki/keylime-tests/

Check what happens when a PR is opened: ansasaki#1

Then, after the PR is registered successfully, it will trigger the internal workflow: https://github.com/ansasaki/keylime-tests/actions/runs/5142302701

Currently, the "check" API is not implemented to link the second workflow with the PR that originated the run.