The pages now receive proper cache tags.
The import now properly clears those cache tags.
That way all corresponding pages will show updated content after import
finished.
We need one test that executes frontend requests and import command.
The separation is therefore removed and tests are streamlined to have a
single parent providing all necessary information and setup.
There might be access to TSFE get_cache_timeout() prior rendering
events.
TYPO3 has a cache for timeout and won't re calculate again.
We therefore need to clear the cache if timeout would change.
That will lead to inconsistent cache information throughout a single
request. But the final cache timeout of the page will be correct. Other
parts might be longer, which probably is fine until they relate to the
events.
Relates: #10500
