PSO: Infer the relative search space automatically

[malun22]

Contributor Agreements

• I agree to the contributor agreements.

Motivation

It is annyoing to set the search space for a sampler. So I added the infer_relative_search_space method to the PSO Sampler to find numeric distributions automatically and add them to the search space.

Description of the changes

• Add infer_relative_search_space to the PSO class
• Notify the user that PSO Sampler cannot process dynamic changes to the search space in the README

[y0z]

LGTM