Add metrics endpoint

spring-app/src/main/java/com/example/demo/DataController.java

@@ -5,12 +5,20 @@ import org.springframework.web.bind.annotation.RestController;
 
 @RestController
 class DataController {
+    private static int callsCount = 0;
+
     @GetMapping("/data")
     SomeData get() {
+        callsCount++;
         var ret = new SomeData();
         ret.setName("ILV Microservice Architecture");
         return ret;
     }
+
+    @GetMapping("/metrics")
+    String metrics() {
+        return "# HELP calls_count Total number of calls\n# TYPE calls_count counter\ncalls_count " + callsCount;
+    }
 }
 
 class SomeData {