fix: make CreateBucketRequest extend from BucketMetadata to allow all…

[ddelgrosso1]

… fields to be set

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Fixes #2454 🦕

[ddelgrosso1]

Making CreateBucketReqest extend BucketMetadata so that the missing fields that are accepted by https://cloud.google.com/storage/docs/json_api/v1/buckets/insert get carried over. I've left the custom fields alone as that would be a breaking change.

[ddelgrosso1]

@danielduhh all tests are existing. Didn't make much sense to add unit tests to test each individual field is settable.