lnrpc: add autopilotrpc subservice

This commit adds a new service lnrpc/autopilot, that is to be used to
communicate with the running autopilot. Currently a RPC for getting the
status of the agent is included, as well as enabling/disabling at
runtime.

lnrpc/autopilotrpc/autopilot.proto

@@ -0,0 +1,34 @@
+syntax = "proto3";
+
+package autopilotrpc;
+
+// Autopilot is a service that can be used to get information about the current
+// state of the daemon's autopilot agent, and also supply it with information
+// that can be used when deciding where to open channels.
+service Autopilot {
+    /**
+    Status returns whether the daemon's autopilot agent is active.
+    */
+    rpc Status(StatusRequest) returns (StatusResponse);
+
+    /**
+    ModifyStatus is used to modify the status of the autopilot agent, like
+    enabling or disabling it.
+    */
+    rpc ModifyStatus(ModifyStatusRequest) returns (ModifyStatusResponse);
+}
+
+message StatusRequest{
+}
+
+message StatusResponse{
+    /// Indicates whether the autopilot is active or not.
+    bool active = 1 [json_name = "active"];
+}
+
+message ModifyStatusRequest{
+    /// Whether the autopilot agent should be enabled or not.
+    bool enable = 1 [json_name = "enable"];
+}
+
+message ModifyStatusResponse {}