Call helper function for killUaa task

[duanemay]

Simplify the killUaa call in integrationTests

To resolve feedback from #3684

Calling an Exec task by iterating and executing its internal actions bypasses Gradle’s normal task execution semantics and is brittle if the task’s actions change. Prefer invoking the Exec task’s exec() directly (or using project.exec) here.

[Copilot]

Pull request overview

This PR refactors the integrationTest task in the uaa module to stop UAA via a local helper function rather than manually invoking the root project’s killUaa task actions, aiming to simplify/process-isolate the shutdown behavior.

Changes:

• Adds an injected ExecOperations holder and a killUaa() helper inside integrationTest.
• Replaces repeated rootProject.tasks.named("killUaa").get().actions... calls with killUaa() calls.
• Adds required imports to support Gradle service injection in the build script.