[Query engine] Support canonical nodes

[levkk]

Support canonical nodes for fall through queries.

[ChronicallyJD]

To describe the idea, instead of throwing an exception on a feature you don't support pass it directly to a predefined canonical source. This ensures minimal failure and expands supportability as you are trying to add features.

It would also be great if you could define a series of canonical DBs. Consider a situation where you have three copies across X that are fully replicated but then you have your aggregated nodes beyond that.