Benchmark improvements and feature requests

**Description**
This is an overarching issue for Benchmarking-related feature requests. It should serve as a central place to discuss possible extensions of the current benchmarking support and figuring what the users want.

**Additional context**
Currently opened issues/requests:
* [Let user set number of collected samples and in-sample iteration](https://github.com/catchorg/Catch2/issues/1711)
* [Let user divide per-iteration timing](https://github.com/catchorg/Catch2/issues/1690) -- Here the idea is that each iteration might be working on an N element batch, and thus the reported iteration times should be divided further.
* [Let user control the measured time](https://github.com/catchorg/Catch2/pull/1701) -- This could also be solved by letting the user ask for more iterations/telling user of more iterations.

Start by reading the three referenced requests: issues 1711 and 1690, and pull request 1701. Compare their proposed benchmarking extensions and the discussion in this issue; completion is not defined because this umbrella issue does not select a specific change or identify files, tests, or an entry point.

Written by the indexing model from the issue text.