[Permission] Layers using WMS/WMTS sources always display in public mode even when private

[bruhnild]

Theory from @cfa: it seems that Django only filters the sources stored in the database, therefore does not take into account the wms/wmts data.

Potentially non-blocking on the project because web map service are often open data but may be problematic in the future.

[submarcos]

I don't know why but it's explicit in code

I'm ok to fix this, If we can set group access, it must be restricted to these group accesses