Push search fixes back to stac-fastapi

[gadomski]

We vendored-and-customized the Search structure, but we should really push those fixes back to stac-fastapi.

[vincentsarago]

FYI I've pushed a lot of changes in https://github.com/stac-utils/stac-fastapi/blob/main/stac_fastapi/types/stac_fastapi/types/search.py (on datetime logic and on type hints)

[gadomski]

Looking at this more, I think the only fix I need to push back is to turn these ValueError and AssertionError into 400s: https://github.com/stac-utils/stac-fastapi/blob/b94c52c2be90cc8945071af0ae9a27945e3a73c1/stac_fastapi/types/stac_fastapi/types/search.py#L37-L38

[vincentsarago]

ref stac-utils/stac-fastapi#835