[TASK] Refactor acceptance tests

typo3/testing-framework got a major release:
composer update typo3/testing-framework ^4.0

* codeception acceptance tests now live in a proper php namespace
* merged installation suites yml files into one
* installer tests are now one suite with different environment settings
* aligned with changes in typo3/testing-framework
* renamed Acceptance test suite to Backend test suite
* removed Admin/Editor steps, replaced with useExistingLogin('role')

Resolves: #85472
Releases: master
Change-Id: Ia049b43f5f9f645dddb509bde557ad83a7ac9023
Reviewed-on: https://review.typo3.org/57461


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>