Add multi-armed bandit-based sampler

[nabenabe0928]

Motivation

multi-armed bandit is another stochastic search algorithm. It is typically for categorical parameters and we would like to add such an algorithm.

Description

• Assume only categorical parameters
• Assume independence of each parameter
• Use $\epsilon$-greedy for this sampler

Alternatives (optional)

No response

Additional context (optional)

No response

[ryota717]

Hi, i tried adding the sampler in #155. Could you review this?