Determine if it is faster to retry an entire transaction from scratch vs. savepoints in cockroachdb

[ecordell]

The recommended way to retry transactions in cockroachdb is to set a special savepoint and rollback to when a retry transaction error is recieved.

The savepointing appears to add a detectible latency to calls that are made retry-able (TODO: get numbers). Depending on the frequency we see retries, it may be worth trading a slower retry (cancel the entire transaction and retry it) in order to avoid savepoints entirely.

This requires testing and metrics to determine a path forward.