[TASK] Add accessibility ci tests with playwright/axe

playwright/axe iterates over a list of web pages and highlights
accessibility issues. This tool is now applied as a CI job to
the TYPO3 Backend where the main backend layout and modules are
being tested.

Usage:

  # CI mode
  Build/Scripts/runTests.sh -s accessibility

  # Run against local instance
  ACCESSIBILITY_BASE_URL=https://t3main.devbox.local/typo3 \
  npm --prefix=Build run accessibility

  # Prepare CI mode, run locally (repeatable command will be printed)
  Build/Scripts/runTests.sh -s accessibility-prepare

Commands executed:
  npm --prefix=Build install --save-dev \
    @axe-core/playwright@4.9.1 \
    @playwright/test@1.45.3

Resolves: #103283
Releases: main, 12.4
Change-Id: Ib1c74027eaacd2a225decd59406d79528f14635e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80557


Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>