This fixes a regression from https://github.com/RIOT-OS/RIOT/pull/20443
which does cause the modules to re-appear in the side panel, but under
the name "Topics" rather than "Modules".
Beginning with doxygen 1.9.8 "Modules" are renamed to "Topics". This
patch adds the new entry to the layout file. Having both, "Modules" and
"Topics" in the layout file should generate similar output for older and
newer doxygen versions.
Add a layout file for Doxygen which has the details section at the
beginning of a page as opposed to the default where the details are
somewhere in the middle.
The initial XML file was generated as specified in the Doxygen
documentation:
```
doxygen -l
```
