Add a benchmark for TransactionManager's transaction throughput

This commit adds a benchmark that allows for measuring the transaction processing throughput of the TransactionManager. The performance is pretty abysmal for now given we're not optimizing for it yet. This does give a baseline idea from where we are starting though and allows for easily verifying the impact of future changes. There are a lot of low hanging fruits such as using long-lived processes, processing the transactions in batches and pipelining the various stages of execution.

Part of #4514 (closed)