add healthcheck service

internal/probe/liveness.go

@@ -0,0 +1,13 @@
+package probe
+
+// Liveness reports the application is alive.
+type Liveness int8
+
+const (
+	// LivenessUnknown reports nothing.
+	LivenessUnknown Liveness = iota
+	// LivenessOk reports service is alive.
+	LivenessOk
+	// LivenessTimeout reports service was unable to answer at a time.
+	LivenessTimeout
+)