Support user information lookup from AD and IPA

This request is an equivalent to what has been done for cern-krb5-conf.

It provides sub-packages for enabling AD cern.ch and IPA ipa-dev.cern.ch domains: cern-sssd-conf-domain-(cernch|ipadev). The default one is set by the cern-sssd-conf-global-(cernch|ipadev)package.

This new modular organisation of the package will be used by the new version for the SSSD Puppet module to support FreeIPA (MALTDS-7).