add public /ping endpoint

Author: CapOfCave

src/main/java/net/developerden/backend/controller/InfoController.java

@@ -0,0 +1,14 @@
+package net.developerden.backend.controller;
+
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+public class InfoController {
+
+    @GetMapping("/ping")
+    public String ping() {
+        return "pong";
+    }
+}