fix: add test case for syncing PTR records

[BobVanB]

Discussion: Responsibility for Restoring Missing PTR Records in Infoblox Webhook

Issue: Inconsistent Handling of PTR Record Restoration

Description of the Problem

We encountered an issue where missing PTR records in Infoblox are not automatically restored. This leads to inconsistencies where an A record exists, but its corresponding PTR record is absent.

Currently, we have observed two scenarios:

1. Stale PTR Records Exist

   • A previous run left behind a PTR record with an outdated IP address.
   • When a new A record is created, the old PTR record should be removed, and a new one should be created.

2. PTR Record is Missing

   • For unknown reasons, the PTR record was removed from Infoblox while the corresponding A record still exists.
   • To maintain consistency, a new PTR record should be created.

Root Cause

There is no clear ownership of PTR record restoration:

• Should external-dns detect and recreate missing PTR records?
• Or should this webhook take responsibility for ensuring that all A records have a corresponding PTR record?

Currently, external-dns primarily manages A records, but there is an expectation that PTR records should be automatically restored when missing. However, without a clear decision on responsibility, this issue can lead to inconsistent DNS states.

Proposed Next Steps

This PR introduces a test case to highlight the problem. Before implementing a fix, we need to decide:

1. Should external-dns proactively restore missing PTR records?
2. Should the Infoblox webhook enforce the creation of PTR records if they are missing?
3. Should the infoblox webhook ditch A,PTR records and use HOST records?

We request input from maintainers and users to determine the best approach.

Impact of This Change

• Raises visibility on the missing PTR record issue.
• Prevents silent inconsistencies in DNS resolution.
• Ensures that A records always have corresponding PTR records (if desired).

Next Actions

• Gather feedback on responsibility for PTR record restoration.
• Decide whether external-dns or the Infoblox webhook should handle missing PTR records.
• Implement changes based on the decision.

[BobVanB]

My colleague has made internal changes to ExternalDNS and the Infoblox webhook. He's currently on vacation, and when he returns, he will create a merge for this.

The main change is that PTR records are now kept in sync, so it's no longer an issue for us if they disappear from Infoblox for some unknown reason.

As far as I'm concerned, this pull request can be closed.