autopilot: rename to Capacity to Balance, define ChannelInfo()

We rename the field Capacity on local channels to Balance, define a new
method ChannelInfo on the manager config that let us query the database
for our latest channels state. Using this we will use the current local
balance instead of the channel capacity when doing allocation
calculations.

autopilot/agent.go

@@ -829,8 +829,8 @@ func (a *Agent) executeDirective(directive AttachmentDirective) {
 	// peers if the connection attempt happens to take too long.
 	delete(a.pendingConns, nodeID)
 	a.pendingOpens[nodeID] = LocalChannel{
-		Capacity: directive.ChanAmt,
-		Node:     nodeID,
+		Balance: directive.ChanAmt,
+		Node:    nodeID,
 	}
 	a.pendingMtx.Unlock()