Feature: support un-publishing specific DNS records

[maleck13]

Use Cases

When migrating an application from one cluster to another, I want to be able to remove the records for one listener within a given cluster/gateway instance without removing the records for all the other listeners in the gateway or removing records for live clusters and gateway, so that I can stop the DNS response sending traffic to one particular gateway instance for a given listener but keep my HTTPRoute etc around to handle / forward on requests that may arrive at the cluster due to DNS caching

In the case where some DNSRecords fail to be cleaned up due to an issue with the DNSOperator, I want to be able to indicate that another controller should remove them so that they are not left in place

Options

Similar to how RateLimitPolicy has a route match option to select HTTPRouteMatch options, we could add something similar for gateway listeners.

use an iteration of the targetRef to be able to select multiple sectionNames

[maleck13]

@mikenairn @philbrookes interested in your thoughts on this type of use case

[maleck13]

@guicassolato We see the need to be able to select a set of section names. I believe you were discussing this also. With the policy machinery, do you see the ability to do this being added as a capability of that? We are debating how we want to solve this type of problem, but it seemed like it was potentially a more generic problem than just DNS

[philbrookes]

This use-case can be covered by sectionName targeting (i.e. target all other sectionNames on the gateway). The ideal longterm solution here is that gateway API introduce an "excludeSectionNames" which can be used to specify specific sectionNames to no longer process). @guicassolato @maleck13