gitserver: dynamically sample honeycomb based on command

Created by: keegancsmith

We are hitting our limits again. By far rev-parse is our most common command. We are currently sending 3500 requests to honeycomb a second just for rev-parse. The next most common is log, which we send 280 req/s.

This commit dramatically scales down the amount of data we send for rev-parse. Most of this information is not that useful. Note: honeycomb does store in the samples the sample rate. This allows us to effectively get count graphs that we can compare.

Note: this is a sourcegraph.com only change.