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.
Use abstract classes to include necessary steps and keep actual test
cases small.
Ensure tests in CI run faster but not installing unnecessary
dependencies. But use pre installed ImageMagick.
