lnrpc+subserver_cfg: add configs for autopilot sub-server

lnrpc/autopilotrpc/config_active.go

@@ -0,0 +1,17 @@
+// +build autopilotrpc
+
+package autopilotrpc
+
+import (
+	"github.com/lightningnetwork/lnd/autopilot"
+)
+
+// Config is the primary configuration struct for the autopilot RPC server. It
+// contains all the items required for the rpc server to carry out its
+// duties. The fields with struct tags are meant to be parsed as normal
+// configuration options, while if able to be populated, the latter fields MUST
+// also be specified.
+type Config struct {
+	// Manager is the running autopilot manager.
+	Manager *autopilot.Manager
+}

lnrpc/autopilotrpc/config_default.go

@@ -0,0 +1,6 @@
+// +build !autopilotrpc
+
+package autopilotrpc
+
+// Config is empty for non-autopilotrpc builds.
+type Config struct{}