MALTDS-137: Fix DNS hostname canonicalisation fallback and move ipa-dev.cern.ch domain/realm mapping to another subpackage

dns_hostname_canonicalisation = fallback does not change the hostname canonicalisation behaviour if rdns = false (as it is in the default /etc/krb5.conf file). This update set rdns = true for the CERN.CH realm as it is currently in most CC7 configurations, to obtain the fallback behaviour we already have for the IPA-DEV.CERN.CH realm.

The .ipa-dev.cern.ch = IPA-DEV.CERN.CH domain/realm mapping was located in cern-krb5-conf-defaults-ipadev package, which is installed only in case IPA-DEV.CERN.CH is the default realm. It makes actually much more sense to put this setting in cern-krb5-conf-realm-ipadev, since this mapping is still true regardless of the default realm.