Add getProjectNumber method to Bucket.java

[alexmos-db]

Is your feature request related to a problem? Please describe.

The Java SDK for GCS does not have a method for fetching the project number even though the value is returned from the describeBucket API. This helper exists on the C# SDK as per: https://cloud.google.com/storage/docs/getting-bucket-metadata#storage-get-bucket-metadata-csharp.

Please also see also JSON API reference: https://cloud.google.com/storage/docs/json_api/v1/buckets#resource

Describe the solution you'd like
Add the method for returning the projectNumber. I intend to open a PR shortly adding the required method.

Describe alternatives you've considered
n/a

[BenWhitehead]

Thanks for the interest (and the PR), I'm reaching out to some folks on the API ownership side of things to see if this field being public is intentional -- last I heard, it was an internal field.

[alexmos-db]

Thanks @BenWhitehead. FWIW, the projectNumber field is available and usable in other language SDKs, here's Python for example: https://cloud.google.com/python/docs/reference/storage/latest/google.cloud.storage.bucket.Bucket#google_cloud_storage_bucket_Bucket_project_number

[BenWhitehead]

I heard from the API team, the field being public is expected to be public, however they need to publish the exact format for how it is exposed for the grpc api. That will hopefully be published soon. Once published your PR will need to be updated to also perform the plumbing for the gRPC transport. I'll followup when it's published.