minor #17597 Modernize Web Server Configuration article (remove obsolete Apache examples, add Caddy) (xabbuh, wouterj)

This PR was merged into the 5.4 branch.

Discussion
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Modernize Web Server Configuration article (remove obsolete Apache examples, add Caddy)

This continues #16104 (which removed old Apache information that advocates bad practices) and fixes #17471 by adding a working Caddy config example.

I've removed most of the Apache 2 version information, we were talking about 2.4 and 2.10, but even Debian oldoldstable (the really long LTS version of Debian) comes with 2.25 already.
I've kept using PHP 7.4 - something that we might want to change when merging up to 6.0. This is done to make the example in the article truely copy-pastable, PHP 7.4 is the current PHP version on the latest Debian version.

Commits
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679bf64 Add Caddy section
33ea1fa Clean-up Apache and Nginx parts
035af33 modernize the web server configuration chapter

Author: javiereguiluz