workload: extend the command-line interface

[jseldess]

PR: cockroachdb/cockroach#37929

From release notes:

• cockroach workload now supports additional command-line parameters to customize the output, to facilitate the integration with third-party testing tools:
  • For tools that wish to observe the metrics more frequently than every second, a new flag --display-every is now supported, which can be used to specify the period between metric reports. This applies to both the JSON and textual output.
  • For tools that require a different output format than the default, a new --display-format argument is supported. For now only the formats "simple" (original output format) and "incremental-json" (RFC3339 timestamps, no summary row) are supported. [#37929][#37929] {% comment %}doc{% endcomment %}