Add cassandra cluster bench

[rukai]

The original idea behind the cassandra_bench example was to be able to run any existing docker-compose.yaml/topology.yaml pair from an example or test as a benchmark.
However that didnt end up working out because tests often have unique topologies, addresses and ports.
Its also a pain to use because you have to figure out how to specify the path to config that it wants.
So im moving our latte based benchmarks to use an example per bench.

To achieve this I've moved our latte wrapper into test-helpers so it can be shared amongst each example.

There are 2 new benches:

• cassandra_cluster_flamegraph
  • I created the shotover instance only after the db init has finished, this ensures we arent profiling shotover while its idle.
  • I also set the rate to 10,000,000, in order to max out the load. Either shotover or latte caps out before then but shotover still continues processing messages fine.
  • Currently doesnt generate the flamegraph that will be done in a follow up
• cassandra_cluster_bench
  • same as cassandra_cluster_flamegraph but it also runs directly against cassandra and compares the performance.

I havent split cassandra_bench into multiple benches yet, but we should do that sometime.