Add Gitaly retry policy

In Gitlab Rails, a retry policy has been in place to account for upgrades. This is exposed in the /allowed endpoint as one of the pieces of information for gitaly connections. Pass this through in a connection option in the gitaly client.

fixes: #831 (closed)

Once gitlab!221553 (merged) is merged, it will start sending over the retry config information. But this can be merged before then since it just falls back to the default retry policy if nothing comes back from the API.

Closes #831 (closed)