Allow skipping all tests if no changes are detected

[ValentinBossi]

The current Change-Aware Test Execution feature provides a couple of mechanisms and extension points the tune the test execution.
What im missing is a setting which allows to skip all tests, when for example a part of the projects readme.md file is updatet, hence no change happened that affects the implementation under test.
Similiar (and in combination?) to spring.modulith.test.reference-commit property a property could activate such a mechanism.

Current existing solutions:

• implement own FileModificationDetector
• configure CI pipeline

Cause this case could be beneficial for many Modulith users an easy solution could make sense.
It also reinforces the idea of skipping tests (to save computational power, etc) when no affected code has changed.

[odrotbohm]

That sounds like a great suggestion. I'd vote for a new property spring.modulith.test.on-no-changes with two values, execute-all and execute-none with the former being the default.

Do you want to take a stab at it?