chroma: fingerprint/submit commands don't lookup or write the item's acoustid_id

### Problem

Currently, only the import process (via `chroma.acoustid_match` writes to the item's `acoustid_id` field. When using `beet fingerprint` or `beet submit` for tracks already in the library, only the `acoustid_fingerprint` field is written.

I confirmed this by looking at the source of the latest master. The cli command calls `fingerprint_item`, and not `fingerprint_task` (or `acoustid_match`), which seems to be only used during the import process.
`item.acoustid_id` is not written in other places.