[TASK] Switch Documentation Rendering to PHP

[Alagts]

You can try out the rendering locally with

make docs

[sbuerk]

We will discuss this dedicated how to proceed and how which way of dispatching we use in standalone fluid (runTests.sh approach / composer script approach / Makefile (with all). Also adding a CONTRIBUTION.md file to describe these kind of things (test execution and so on).

Thus remove the Makefile from this PR for now and integrate the CI run for it first and directly and not postpone this change until decision of the topics above are made.

[Alagts]

I removed the Makefile. Now, you can try out the rendering locally with

docker run --rm --pull always -v $(pwd):/project -it ghcr.io/typo3-documentation/render-guides:latest --config=Documentation

[s2b]

Thanks! :)