feat: repalce deprecated .permissionPolicy with .permissionsPolicyHeader

Author: jornfranke

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 * Backend: Hardened configuration of actuator and [improved configuration documentation](./backend/docs/CONFIGURE.md) around it
 * Backend: Include H2 in-memory database only when using bootRun (Gradle: developmentOnly) and not when deploying as it is only for local development. Real database drivers (e.g. postgres JDBC) for production should be included using implementation.
+* Backend: Configure HTTP Security Header permission policy with .permissionsPolicyHeader as .permissionPolicy is deprecated
 * Backend: Gradle Plugins: Spring Dependency Plugin 1.1.7, Spotless 7.0.1
 * Backend: Build tool Gradle 8.12