Add developer productivity scripts and document testing guidelines

[unmarshall]

How to categorize this issue?
/area dev-productivity
/area testing
/kind enhancement

What would you like to be added:
Introduce the following capabilities:

• Add capability to stress test to help de-flake tests (script and/or make target) - for both unit and integration-tests
• Add capability to start envtest separately and run integration-tests targeting it. This helps analysing the state of the resources and helps in debugging tests.
• Add capability to check if there are incompatible api changes.
• Add a common formatter (make target) for all source files to ensure uniformity on how all code needs to be formatted.
• Add a doc on testing guidelines

Why is this needed:
Enhance developer productivity