[Junit5 extension] Run test multiple times for the same flag with different values

Sometimes, you want to ensure that your code behaves the same way for all code paths, even if different feature flags are involved.

Junit5 has parameterized tests to run multiple tests based on a source. This approach is not feasible for us, as it only generates an array of possible argument sets.

We need to find a way (maybe with our annotation) to create such tests. The cartesian test extension of JUnit Pioneer can be an inspiration for this https://github.com/junit-pioneer/junit-pioneer/blob/main/src/main/java/org/junitpioneer/jupiter/cartesian/CartesianTest.java

Start by reading the JUnit 5 parameterized-test documentation and the linked JUnit Pioneer CartesianTest.java for comparable extension behavior. Clarify how the existing annotation and feature-flag values should be represented, then define tests showing that one flag can run with multiple values and that all intended paths execute.