[FEA] raft-ann-bench auto-generate CLI documentation

[fy]

Is your feature request related to a problem? Please describe.

The documentation is not up-to-date. For example, the default value for --search-mode is actually latency as of now.

Describe the solution you'd like

The CLI documentation should be auto generated. Even better, the detail explanations could be part of the code, and thus auto-generated. We can consider using typer for the CLI interface, which provides a convenient way of generating the doc in markdown (details here).

Describe alternatives you've considered

We use pydoc, but I am not sure if pydoc can generate documentation for CLIs.