Add GAR support

[Alphasite]

This is adding google artifact registry support; i have manually tested it and it appears to work.

❯ ./leftovers-darwin-amd64 --filter bacon --gcp-service-account-key ~/Downloads/GSAK.json -i gcp --type="repository" --debug 
Listing Repositories for region asia-northeast1...
Listing Repositories for region europe-west12...
Listing Repositories for region southamerica-west1...
Listing Repositories for region asia-south2...
Listing Repositories for region asia-southeast2...
Listing Repositories for region europe-west9...
Listing Repositories for region northamerica-northeast1...
Listing Repositories for region us-east5...
Listing Repositories for region asia-northeast2...
Listing Repositories for region asia-northeast3...
Listing Repositories for region us-west2...
Listing Repositories for region asia-east2...
Listing Repositories for region asia-south1...
Listing Repositories for region europe-central2...
Listing Repositories for region us-east1...
Listing Repositories for region us-west3...
Listing Repositories for region asia-east1...
Listing Repositories for region australia-southeast1...
Listing Repositories for region me-central1...
Listing Repositories for region me-west1...
Listing Repositories for region us-east4...
Listing Repositories for region europe-north1...
Listing Repositories for region europe-west2...
Listing Repositories for region europe-west6...
Listing Repositories for region southamerica-east1...
Listing Repositories for region europe-southwest1...
Listing Repositories for region europe-west1...
Listing Repositories for region europe-west8...
Listing Repositories for region us-south1...
Listing Repositories for region us-west1...
Listing Repositories for region asia-southeast1...
Listing Repositories for region australia-southeast2...
Listing Repositories for region europe-west3...
Listing Repositories for region europe-west4...
Listing Repositories for region northamerica-northeast2...
Listing Repositories for region us-central1...
Listing Repositories for region us-west4...
[Artifact Repository: projects/nishadm/locations/us-west2/repositories/bacon-repo] Delete? (y/N): y
[Artifact Repository: projects/nishadm/locations/us-west2/repositories/bacon-repo] Deleting...
[Artifact Repository: projects/nishadm/locations/us-west2/repositories/bacon-repo] Deleted!

[Alphasite]

meant to open this as a draft, sorry.