This avoids gossip spam and false positive Discord notifications
when a connected node catches up and late observations are made.
Change-Id: If9562661487d3d3d5138d27298b005f278f9e9ce
Optional metadata for debugging. Allows tying a received observation
to an on-chain transaction even if the node missed the observation.
Change-Id: Ie50c10c8ab7f65469555674d90645f91092fb2e3