Looking to contribute nested field filtering and DB optimization

[mlissner]

Hi!

We use this package on our API at CourtListener.com, where we provide a public API used by many people and organizations.

We're getting two related requests from users that we want to address:

1. Folks want to filter nested fields as described in https://github.com/dbrgn/drf-dynamic-fields/issues/15. We think this would be easy from an API perspective (just use double-underscores to indicate sub-items).

2. Folks want this package to optimize the queries sent to the DB (probably using django's defer() method on the backend).

   This change is needed because we have a field in our API that contains the text of large documents and some users do not want to pull that from the DB in the first place.

I notice that this package hasn't been updated in several years. If we provide a clean PR with tests for each of these features, would that be welcome? If not, I think our plan will be to make a little fork with the functionality we need.

Thank you!