PR for autoware.universe repository now needs a tag to run CI

[mitsudome-r]

Due to the issue with GitHub runners not having enough disk space to run the CI in the autoware.universe repository, we have replaced it to use a self-hosted runner with larger disk space. In order to lower the security risk of running CI in the self-hosted runner, we have also added the guard to block running build-and-test-differential job to only run when the run-build-and-test-differential label is added to the PR. (Labels can be only added by a developer added to Autoware Foundation GitHub Organization.)
If you are a PR reviewer, please add the label after checking that there is no malicious code in the PR for the CI to pass.

Please contact me if you have any questions.