Query node registry subgraph to get list of nodes, with ability to override it

[neekolas]

(written by @mkysel )

Right now, as of XIP-49, the client is responsible for picking the originator node. It should do so using the preferred node algorithm (#1547).

The source of truth for the pool of all available nodes is in the blockchain contract.

The client needs to fetch this list and pick a node to send the message to.

There might be better solutions that to directly parse the blockchain available.

NOTE: If the client picks the wrong node, it won't lead to catastrophic failure. It might lead to slight message misordering. As such, the list can be slightly outdated.