put the documentation from the man page for fusiondirectory.conf into the official web documentation

hello,

we need to put a section detailing what can be configured in the fusiondirectory.conf file into the official documentation.

It should bed added after the section web-setup https://fusiondirectory-user-manual.readthedocs.io/en/1.4/fusiondirectory/install/web-setup.html

The section should be named fusiondirectory.conf configuration