added post request to achieve login response with tokens

backend/src/main/java/com/vaessl/app/dto/ConnectionRequest.java

@@ -0,0 +1,9 @@
+package com.vaessl.app.dto;
+
+import jakarta.validation.constraints.NotBlank;
+
+public record ConnectionRequest(
+        @NotBlank(message = "App URL is mandatory") String appUrl,
+        @NotBlank(message = "Username is mandatory") String username,
+        @NotBlank(message = "Password is mandatory") String password) {
+}