Add single node async benchmark execution to integration tests

[awonak]

This also refactors the flag for no-dataflux since that option is mutually exclusive with the other checkpoint save options.

Internal issue: b/369839708

• Tests pass
• Appropriate changes to documentation are included in the PR

[awonak]

I spoke with @jdnurme about having a future follow-up PR to have the async benchmarks measuring end-to-end workloads instead of individual save_checkpoint calls here. This PR is still useful by having the new async checkpoint code executed in our integration tests, but to fully close out b/369839708, we would ideally like to have an end-to-end benchmark. This new benchmark test work is documented in b/371056459.