PaymentForwarded should include counterparty nodes

[TheBlueMatt]

It just includes ChannelIds, which is generally fine (if you're forwarding hopefully it's not over 0conf channels), but technically ChannelIds aren't unique (for v1 0conf opens) so we need to include the counterparty node ids. I mean also as should because they're, like, useful.

[tnull]

When we do this it might make sense to keep it consitent with the channel ID and user channel ID fields, i.e., introduce next_node_id and prev_node_id fields, IMO.