Explore alternatives to Apache to run core tests

Problem/Motivation

As maintainer of freeunit.org (the LTS fork of Nginx Unit) and user of it not only for PHP and Drupal I find more performant nowadays even comparing to php-fpm so we can cut viable amount of time for running tests.

Another option is https://rapira.rs/ which is beating all other app-servers but not yet tested with Drupal

Proposed resolution

- create CI images to run core tests using it (remember that testing site is living in subdirectory)
- create core MR to prove it can run tests (htaccess tests should be fixed or skipped)
- tune PHP and other settings in CI to get maximum perf and decide if the win of replacement still makes sense, a-la 10% diff
- compare numbers and find a way to promote it

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet