storage*: origin_get(Iterable[str]) -> Iterable[Optional[Origin]]

This:

• drops the legacy behavior (no more input as list of dicts or even one dict).
• aligns with other _get endpoints (only 1 iterable of identifiers as input,

here the origin urls).

• migrates towards returning an iterable of optional origin model

objects (again the optional part is alignment with existing get endpoint)

Related to T645