Closes#1731
Implements the admin `CreateBucket` (`PATCH /:bucket/create`) endpoint and CLI command, which create a new bucket with the provided owner access key ID. The endpoint internally calls the S3 `CreateBucket` API, storing the new owner information in the request context under the `bucket-owner` key. This value is then retrieved by the S3 API layer and the backends.
The endpoint uses the custom `x-vgw-owner` HTTP header to pass the bucket owner access key ID.
The admin CLI command mirrors `aws s3api create-bucket` and supports all flags implemented by the gateway (for example, `--create-bucket-configuration`, `--acl`, `--object-ownership`, etc.).