Cannot globally override DataFetcher's on custom operations/fields/properties

Overriding DataFetcher's currently is only supported on the automatically provided operations, and is not possible on custom operations or fields/properties.

This is cumbersome when dealing with a large object graph where a given entity type might be an associated property in numerous places, and where you want to restrict the data returned for that type, but not have to supply a custom DataFetcher everywhere the type is used.

Start by locating the DataFetcher override handling and the code paths for custom operations, fields, and properties. Determine how a global override should apply across an entity type, then verify that the override works consistently wherever that type is used in the object graph.

Written by the indexing model from the issue text.