build(deps): bump com.netflix.dgs.codegen in /backend

Bumps com.netflix.dgs.codegen from 7.0.3 to 8.1.0.

---
updated-dependencies:
- dependency-name: com.netflix.dgs.codegen
  dependency-version: 8.1.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/build.gradle.kts

@@ -5,7 +5,7 @@ plugins {
     id("org.springframework.boot") version "3.4.4"
     id("io.spring.dependency-management") version "1.1.7"
 
-    id("com.netflix.dgs.codegen") version "7.0.3"
+    id("com.netflix.dgs.codegen") version "8.1.0"
     id("org.jlleitschuh.gradle.ktlint") version "12.2.0"
 }