dataloader caching for custom queries with a Clause

[lolopinto]

await Promise.all(
[1, 2,3,4,5].map(() => 
  Foo.loadCustom(viewer, query.Eq('index', val)))
);

would previously make 5 queries to the db. After this change, it would make one.

Now, we put custom clause queries behind a dataloader. We only do that for custom queries that use Clause. Not for queries with a raw sql query or a parameterized query

previous context on custom queries: #1049, #1122