Block type search functionality for LLM agentic interactions

[yue-here]

A common LLM use case is probably 'find all samples containing data of type X' so to facilitate LLM API interactions, I suggest adding 'block_ids' or similar in the return to get_items() which outputs a list of block ids ['xrd', 'raman', ...]

[ml-evs]

This is a limitation of the underlying server API atm, but we can add it quite easily. I'll transfer the issue there and get something out soon.