TUN-2117: read group/system-name from CLI, send it to edge

tunnelrpc/tunnelrpc.capnp

@@ -57,6 +57,17 @@ struct CapnpConnectParameters {
     tags @3 :List(Tag);
     # release version of cloudflared
     cloudflaredVersion @4 :Text;
+    # identifier for this cloudflared instance
+    scope @5 :Scope;
+}
+
+struct Scope {
+    value :union {
+        # Standalone instance
+        systemName @0 :Text;
+        # Associated with a group of identical cloudflared instances
+        group @1 :Text;
+    }
 }
 
 struct ConnectResult {