T3008

Depends on D13390

Parse incoming txs seen by the websocket to see whether or not they are valid alias txs. If they are, add them to a new database collection 'pendingAliases.' Make this collection viewable at the API endpoint /pending

Note: pending aliases are not checked against the full history of aliases. If they happen to be registered earlier, then we also want to block them from being registered as pending. No real harm in 'double counting' them this way. It's possible someone manually creates an alias registration tx that would be invalid once confirmed bc it is already taken, and this gets added to the pendingAliases table. NBD. After the block is found, such aliases will not be validAliases.

npm test and pass
node index.js
Register some a couple of aliases
Visit localhost:5000/pending and see them there