core/remote: Fix getDirectoryContent's query index
core/remote: Fix getDirectoryContent's query index

  The `RemoteCozy.getDirectoryContent()` method's query to fetch the
  content of the given remote directory was not declaring `dir_id` as an
  indexed field although it is used in the selector.
  This means the CouchDB request won't use the appropriate index and the
  query will be very slow, at best.

  Simply declaring the field as part of the indexed fields and the sort
  fields will improve the query response time.

  We also reduce the limit of the query as we've encountered timeouts on
  some Cozy with the 10000 documents limit.

cozy-labs/cozy-desktop,cozy-labs/cozy-desktop,cozy-labs/cozy-desktop,cozy-labs/cozy-desktop