The goals are:
* To have better result in the GetCapabilities URL without having to fill it in the Project configuration
* Be able to be set by an integrator with environment variable or by providing headers from a proxy
The server resolution will use the following order:
- Value defined in the project per service.
- The ``<service>_SERVICE_URL`` environment variable.
- The ``SERVICE_URL`` environment variable.
- The custom ``X-Qgis-<service>-Servcie-Url`` header.
- The custom ``X-Qgis-Service-Url`` header.
- Build form the standard ``Forwarded`` header.
- Build form the pseudo standard ``X-Forwarded-Host`` and ``X-Forwarded-Proto`` headers.
- Build form the standard ``Host`` header and the server protocol.
- Build form the server name and the server protocol.
Defined a new QGIS Server setting environnement `QGIS_SERVER_DONT_LOAD_LAYOUTS` to do not load layouts when QGIS Server reads projects.
This variable will disable QGIS Server GetPrint capabilities.
Allow to override the default behavior in case of
bad layers (which is to invalidate the whole project).
When set to TRUE, the bad layers are skipped and the
project is considered available.
Followup #8922
