Title: #5486: krb5: allow to use subdomain realm during authentication
:feature: `krb5_use_subdomain_realm=True` can now be used then subdomain user
principal names with different upnSuffixes not found in parent domain as it
requires to be supported on serverside, but not implemented in samba yet.
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/5486/head:pr5486
git checkout pr5486