update backgrounds in sample config to use IGN services

[landryb]

been using them in production for a while...

@MaelREBOUX @jusabatier @pierrejego your opinion ? after all that's just the default/sample config.

for me the sample existing config bails out when generating a BP:

2022-09-14 15:17:03,869 DEBUG [org.georchestra.cadastrapp.service.ImageParcelleController] /cadastrapp/services/getImageBordereau - nouser - norole - noorg - Create webMapServer : http://osm.geobretagne.fr/service/wms?VERSION=1.1.1&Request=GetCapabilities&Service=WMS
2022-09-14 15:17:04,077 ERROR [org.georchestra.cadastrapp.service.ImageParcelleController] /cadastrapp/services/getImageBordereau - nouser - norole - noorg - Error while getting basemap image, no basemap will be displayed on image
org.geotools.ows.ServiceException: Error while parsing XML.
...
        at java.lang.Thread.run(Thread.java:829) [?:?]
Caused by: org.xml.sax.SAXParseException: The element type "hr" must be terminated by the matching end-tag "</hr>".
        at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:204) ~[?:?]

(but there's no <hr> element in the getcapabilities ?)