Add support for slot-based nested GraphQL queries

[buffalojoec]

Motivation

We could go completely bananas with the GraphQL schema, and allow block queries anywhere there's a slot in a response.

Similar to how we've replaced any address fields with a queryable account, we can do the same for any slot fields, allowing even more query-chaining!

Details

It's actually pretty easy to implement, it would just require some minor redundancy for slot other than just being a bigint. This would behave exactly like account, where we're inserting address and only requesting the RPC if any other field is queried.

query myQuery {
  slot {
    slot
  }
}