[TASK] Use own configuration files for tests

[lukaszuznanski]

Resolves: #902

[oliverklee]

We're already using PHPUnit 9. So we should switch to coverage and include here.

[sbuerk]

@oliverklee @lukaszuznanski

Little bit late. TBH the bootstraps should also not be used from the the typo3/testing-framework vendor folder and copied to the project.

The background is, that there are scenarious where it's needed to make some changes based on the project/extension.

Beside this, the chosen location is kind of flattered. Configuration for all tools should be collected in one place and not distributed throughout a lot of places (and not the root folder)
to have a clean and "one place" to look it up. But that is maybe more a personally flavour - where I highly disagree to take this places as best practice.

[oliverklee]

Thanks, I've created #1082 for moving these files.