Testing load based on time and steps

[pesterev]

According to this issue, we should add a step-based testing load.

My suggestion is to enhance the oneshot command:

• [ ] Perform a pool of operations concurrently.
• [ ] Perform in several steps.
• [ ] Timeout for every step.
• [ ] Action on errors.

[timofeevmd]

explanations for the first two paragraphs

At the first stage, I enter 60 (in the context of the Ultimate Thread Group meter) parallel operations for 10 seconds

Each operation, which includes a sequence of transactions, of the first stage will be performed cyclically for 610 seconds independently of each other