lnrpc/peers: skeleton logic for updateNodeAnnouncement

Basic logic for the endpoint:

- Get the current nodeAnn information
- Calculate modifications
- Apply modifications
- Return changes

.golangci.yml

@@ -17,6 +17,7 @@ run:
     - chainrpc
     - dev
     - invoicesrpc
+    - peersrpc
     - signrpc
     - walletrpc
     - watchtowerrpc