Development: Add annotation to disable thread group check

[bensofficial]

Problem

When testing JavaFX exercises with TestFX, the tests fail because TestFX spawns additional threads in the thread group. These threads are terminated during thread group validation, which disrupts the TestFX testing process.

Solution

Introduce a new optional annotation, @DisableThreadGroupCheck, that disables the thread group check when applied. This prevents the termination of threads spawned by TestFX, allowing the testing process to complete without interruptions.

You might have a look at how this is used for testing JavaFX exercises: https://github.com/bensofficial/javafx-example

[Hialus]

Changes look good to me. Would be great if this is merged soon, so we can use it :D