Feature: relationship filtering

[florian-lefebvre]

Currently, we can add relationship between 2 collections, for any entry.

It would be great to allow applying filters, for instance:

fields.relationship({ label: "Category", collection: "categories", filter: (entry, collectionEntry) => entry.locale === collectionEntry.locale })

To achieve this, I think types from collections must be properly passed to each other in order to type properly collectionEntry (as well as collection)