Add OpenLDAP support in unit tests

.gitlab-ci.yml

ldap_server_entries_add.ldif

ldap_server_entries_cleanup.ldif

ldap_server_entries_modify.ldif

tests/test_mail.py

tests/test_mfa.py

tests/test_oauth2.py

tests/test_role.py

tests/test_selfservice.py

tests/test_session.py

tests/test_user.py

tests/utils.py