Add benchmarks tutorials

[y0z]

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Motivation & Description of the changes

This PR adds tutorials on benchmarks.
Please merge optuna/optunahub#73 before merging this PR since this PR requires the optunahub.benchmarks module that has not been merged into the master branch of optunahub.

[nabenabe0928]

I think here needs to be updated as well.

optunahub-registry/recipes/002_registration.py

Line 77 in 3528121

- ``tags`` (list[string]): The package tags. It should be a list of strings. The tags must include ``sampler``, ``visualization``, or ``pruner`` depending on the type of the package. You can add other tags as needed. For example, "['sampler', 'LLM']".

[y0z]

#202 (comment)

Thank you. I addressed it.

[y0z]

All suggestions have been applied. PTAL.

[nabenabe0928]

Almost LGTM!
As the last thing is to make the doc a bit more consistent and the other parts follow the same convention, I will commit it by myself and will merge this PR!