add max-os-threads flag

[dogancanbakir]

Proposed changes

Closes #5605

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[Mzack9999]

What do you think if we make this automatic to a reasonable larger amount than the estimated maximum parallelism, for example something like the result of 3 x (concurrency x bulk-size x payload-concurrency + js-concurrency + probe-concurrency)

[dogancanbakir]

We can do that, but I believe overriding it should be an option.