title: want to send deltas to server using ra-data-json-server
body: <p>we're using react-admin with a jsonServerRestClient from ra-data-json-server.  We've encapsulated it to handle GET_MANY a little differently, so we already have a touchpoint there to control what goes to the server.  </p>
  
  <p>Going forward we would like to be able to send a delta of changes when an item is modified, as some items (in our case, groups) have 4k+ members in them.  </p>
  
  <p>While we could save the raw objects to local storage when they come into our REST client and use that info to create a delta upon save, the state and reducers should have that info already somewhere else, right?  </p>
  
  <p>So what files should I look at to see how to modify what gets sent to the REST client during modify events?</p>