Implement writeWithResponse in FakeStorageRpc

[rbraeunlich]

Is your feature request related to a problem? Please describe.
With Pull Request #135 the FakeStorageRpc class extends StorageRpcTestBase and now google-cloud-storage is a needed dependency when using the class in tests. In google-cloud-storage the implementation of BlobWriteChannel has been changed a month ago (https://github.com/googleapis/java-storage/pull/269/files#diff-8561e6a9172119adf8e882a3f5298d6bR69) so that flushBuffer now calls writeWithResponse instead of write.
writeWithResponse is neither implemented in FakeStorageRpc nor in StorageRpcTestBase, which causes my tests to crash now, which didn't happen before.

Describe the solution you'd like
Please implement the method. Since the response is a StorageObject it shouldn't cause any problems.

Describe alternatives you've considered
My workaround is now to set my dependency to google-cloud-storage fixed to 1.110.0. But this pins me on this version.

[MartinHaeusler]

The same thing happened to me as well. Can't upgrade my cloud storage client until this issue is resolved...