Test lighttpd was build with lua support

[yubiuser]

What does this PR aim to accomplish?:

Adds a test to check if the installed lighttpdwas compiled with lua support. In the light of possible upcoming changes regarding lighttpd, this test might become useful

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[PromoFaux]

I don't think this is required at the moment - but we can come back to it should we need to in the future.

The recent changes in #5065 and #5075 went the way of simplifying the config, rather than introducing the lua script via mod_magnet

[gstrauss]

As @PromoFaux mentioned, this does not seem to be needed at the moment, though it is an option that is mentioned at pi-hole/docs#824 (awaiting review)

FYI: lighttpd reporting that it was built with lua support does not necessarily mean that mod_magnet is available. The packager may have built lighttpd with lua support, but then made a separate package containing mod_magnet (e.g. lighttpd-mod-magnet) dependent of the lighttpd package. That separate package might not be installed on the system.

A more sure-fired way to determine if mod_magnet is available:

• Attempt to install the appropriate package on the system
  (lighttpd-mod_magnet or lighttpd-mod-magnet on many systems; lighttpd-modules-lua on Debian 11 and later)
• Create /tmp/test.conf

server.document-root = "/tmp"
server.modules = ("mod_magnet")

• Run lighttpd -f /tmp/test.conf -tt. If the command exits success (0), then mod_magnet is available. If the command exits non-zero, mod_magnet is not available.

[yubiuser]

@gstrauss Thanks for the extended and improved test example.
As there is currently not *.lua config planed anymore, I'm going to close the PR. We can revive it later if needed.