* udm_dns_record: Fix handling of PTR records (#3244)
Before, it was not possible to manage PTR records in Univention DNS,
due to broken zone lookups and improper used parameters of the object.
This patch fixes the PTR handling, allowing both v4 and v6 entries.
* udm_dns_record: [doc] add changelog fragment
* udm_dns_record: [fix] validation errors
* udm_dns_record: import ipaddress module conditionally (#3244)
* udm_dns_record: fix sanity check error, improve doc (#3244)
* udm_dns_record: Improve changes to meet community standards (#3244)
