Add version field to GetInfo RPC endpoint

This is inspired by the Bitcoin RPC `getnetworkinfo` endpoint which also
includes version information:
https://bitcoin.org/en/developer-reference#getnetworkinfo

rpcserver.go

@@ -1247,6 +1247,7 @@ func (r *rpcServer) GetInfo(ctx context.Context,
 		Uris:                uris,
 		Alias:               nodeAnn.Alias.String(),
 		BestHeaderTimestamp: int64(bestHeaderTimestamp),
+		Version:             version(),
 	}, nil
 }