workload: handle ambiguous errors

Clients are expected to handle ambiguous errors; for instance, see our own documentation:

* [cockroachlabs.com/docs/stable/transaction-retry-error-reference](https://www.cockroachlabs.com/docs/stable/transaction-retry-error-reference)
* [cockroachlabs.com/docs/stable/common-errors#result-is-ambiguous](https://www.cockroachlabs.com/docs/stable/common-errors#result-is-ambiguous)

Despite that, our very own `workload` does not handle these errors, leading to occasional roachtest failures that should not have happened.

We want `workload` to be able to handle these errors whenever possible (retrying when safe to do so). It might not be possible to completely eliminate these errors from bubbling up to the caller every time; each workload should be updated independently.

Jira issue: CRDB-30113