PHP not supported anymore by the end of the year

The website in this repo uses PHP which is deprecated on https://eclipse.dev/ (see [1]).

As far as I see the files are basically unused, with the exception of index.php, which just redirects to our project website on eclipse.org. Even after deprecation the openPASS documentation hosted in content/html... should still be available. No PHP is used there.

Still, we should update according to [1] (hugo template) and maybe also think about the interaction between https://eclipse.dev/openpass/, https://projects.eclipse.org/projects/automotive.openpass and https://openpass.eclipse.org/ respectively.

@adascri @tplatzer @barbarakohn

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[1] https://www.eclipse.org/lists/eclipse.org-committers/msg01460.html