lnrpc/peers: skeleton logic for updateNodeAnnouncement

Basic logic for the endpoint:

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

lnrpc/peersrpc/peers.yaml

@@ -1,2 +1,8 @@
 type: google.api.Service
 config_version: 3
+
+http:
+  rules:
+    - selector: peersrpc.Peers.UpdateNodeAnnouncement
+      post: "/v2/peers/nodeannouncement"
+      body: "*"