Split collection content into own files

[Dominic-Marcelino]

Is your feature request related to a problem? Please describe.
The snapshot feature splits up the collections, fields and relations each into single files. This makes it easy to read, review and merge.
The collections content instead get's stored in a single file per collection, containing all entries. On growing content this makes it pretty hard to read and review changes.

Describe the solution you'd like
I think the collections content could be stored as a file per item (named by the id), grouped in a folders named by the collection. This would align well with the snapshots and create smaller, easier to maintain.

-- directus-config
  -- collections
    -- collection_name_1
      -- item_1.json
      -- item_2.json
   -- collection_name_2
      -- item_1.json
      -- ...