refactor: customize HTTP transport for GCS client

[nblair]

This change set is the result of some investigation on the poor throughput issue (see #1).

It includes the following:

• Upgrades google-cloud-storage to latest release
• Setup the ApacheHttpTransport to use a pooling client connection manager. This addresses an issue observed with the default connection manager; after a period of inactivity, the client would fail to connect to the google API endpoint and not retry. This implementation does successfully retry when connections are severed. This change comes with a caveat in that it requires us to use deprecated HTTP Client constructors instead of their current equivalents.
• Improve the performance of hard delete by skipping an unnecessary prior GET.
• Lean down object read requests to only retrieve the MEDIA_LINK field (at this time all other GCS object attributes aren't used by this implementation).

[nblair]

I'll note here too that I don't believe this conclusively resolves #1, but casual observations show we are headed in the right direction. This project would benefit from some tooling to automate performance testing in a full NXRM deployment in Google Cloud.

[nblair]

googleapis/google-http-java-client#364 describes the issue necessitating the use of deprecated constructors - if we use the current means for constructing our own HttpClient to pass into the ApacheHttpTransport constructor, we get the same UnsupportedOperationException .