[R] Add GCS tests using testbench

[asfimport]

Followup to ARROW-16510. That PR added the bindings and basic R tests that don't require a live GCS connection. GCS has a "testbench" service you can run on localhost to test, like how we use minio to test S3. See the Python bindings PR for reference on how to set it up and run it, as well as some tests we could add: #12763

Reporter: Will Jones / @wjones127
Assignee: Will Jones / @wjones127

Related issues:

• [C++] Reject trailing slashes on file path (is blocked by)

PRs and other links:

• GitHub Pull Request #13542

_{Note: This issue was originally created as ARROW-16879. Please see the migration documentation for further details.}

[asfimport]

Neal Richardson / @nealrichardson:
Issue resolved by pull request 13542
#13542