Add a manual dry-run job with CE repository .triage-policies.yml
For now the manual dry-run job is using the
.triage-policies.yml in this repository, while it's nice to run this against target repository with a branch configuration via variable.
This way we could trigger a manual pipeline with something like
$PROJECT_BRANCH=gl-triage to target the current triage polices in CE.
$PROJECT_BRANCH=gl-triage-MR we could even trigger this against an arbitrary branch for reviewing the effect on CE merge requests.