Don't increment the zone serial if its contents has not changed

[kiran pawar]

Updates that do not lead to an actual change in the zone contents should not increment the SOA serial.

For example, setting the same recordset to the same value over and over again should not have an effect on the SOA serial. Our client might want to make sure infra changes should match with IaC and so there are many updates(e.g. 50-60) at once. The current behaviour results into an unnecessary cascade of zone replications.

We should track those unchanged zone updates and do not increment serial.

[Erik Olof Gunnar Andersson (eandersson)]

Is this as much of an issue in Bobcat where zone serial are incremented in batches meaning that if your client does 50 updates within a 5 second window it would only generate a single update on the DNS server?

[kiran pawar (kpdev)]

We have not tested with bobcat, I will try to backport you patch(https://review.opendev.org/c/openstack/designate/+/871255) and see if helps.