consensus roothash messages

[pro-wh]

roothash messages are small structures that a runtime can send to communicate with the consensus layer. they are agreed upon for each runtime block. we'll see the messages themselves in the proposal for that block, i.e. in the first executor commit for the round. the consensus layer processes these messages when the block gets finalized, which produces a result for each message. in cobalt and below, the roothash consensus app emits an event for each message. in damask and up, the results are stored on chain, and you use a roothash "get last round results" query to look up the results.

in this feature, we add a roothash_messages table with tracked runtimes' messages and results. either of the message or result may be absent, as they can be disseminated in different consensus blocks.

[mitjat]

Thank you! LGTM in general; I just have a few questions where I want to make sure the answers are not hiding surprises.