misc: add an API to set the client app's resource directory path

This approach allows client apps that install ringtones (and any other resources) in custom locations to specify that directory at runtime. This will take precedence over the build time data directory supplied for platforms which install to a fixed path.

https: //git.jami.net/savoirfairelinux/jami-client-qt/-/issues/1619
Change-Id: I81616f79196e645a5ad677d6956be6a2ffcd976a