Support optimization of multiple points in batch spaces

[khurram-ghani]

Related issue(s)/PRs: None

Summary

Add support for batch optimization of multiple points per region/subspace in a TaggedMultiSearchSpace collection.

Fully backwards compatible: yes

PR checklist

• [X] The quality checks are all passing
• [X] The bug case / new feature is covered by tests
• [X] Any new features are well-documented (in docstrings or notebooks)