Integrate QGIS Server setup notes

[rldhont]

To help user install lizmap-web-client, it will be great to integrate QGIS Server setup notes https://www.itopen.it/qgis-server-setup-notes/ from @elpaso

[pcav]

I think we can just link to official QGIS docs, to avoid duplication.

[nboisteault]

@pcav yes I'm going to rewrite this part of the doc to make it simpler.

[pcav]

Thanks @nboisteault
Count on me if you need some help.

[Gustry]

QGIS server doc has been removed from the repository, in favor of the main QGIS server documentation https://docs.qgis.org/3.28/en/docs/server_manual/

https://docs.lizmap.com/current/en/install/pre_requirements.html#id1

Only specific part for Lizmap has been kept.

The only missing part is Py-QGIS-Server.