Use self:: instead of AuthService:: in AuthService

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Deprecate authCountUsers, introduce getUsersCountFromAuth and getUsersCountFromConf

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Introduce userExistsInConf in AuthService

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Add supportsUsersPaginationInConf

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>