feat: add agent acks to in-memory coordinator (#12786)

When an agent receives a node, it responds with an ACK which is relayed
to the client. After the client receives the ACK, it's allowed to begin
pinging.

enterprise/coderd/workspaceproxy.go

@@ -658,7 +658,7 @@ func (api *API) workspaceProxyRegister(rw http.ResponseWriter, r *http.Request)
 			if err != nil {
 				return xerrors.Errorf("insert replica: %w", err)
 			}
-		} else if err != nil {
+		} else {
 			return xerrors.Errorf("get replica: %w", err)
 		}