[distrubution-spec] Add custom transport adapter to client

[vsoch]

I want to check on what are the reasons/ advantages to creating a custom transport adapter, as is done here. The python requests library allows for definition of a similar thing: https://requests.readthedocs.io/en/master/user/advanced/#transport-adapters. @jdolitsky sorry for the multiple pokes today! If you have a few minutes in the next week or so to give a quick answer, it will definitely be helpful! For the meantime I'm going to skip creating the custom adapter.

[jdolitsky]

@vsoch it is probably not needed. In looking in the differences, I'm seeing DisableCompression: true,, which I think turns off the header Accept-Encoding: gzip that the Go http lib adds automatically. We were trying to control all headers sent for conformance reasons, but its probably unnecessary/overkill.

[vsoch]

Closing because not needed!