Added backend and fixed openapi generation

backend/src/main/java/com/alttd/altitudeweb/AltitudeWebApplication.java

@@ -0,0 +1,13 @@
+package com.alttd.altitudeweb;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class AltitudeWebApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(AltitudeWebApplication.class, args);
+    }
+
+}