Add advanced test for DNSPolicy Health Checks

[averevki]

Summary

Test if the unhealthy endpoint was correctly removed from the list of available endpoints in DNSRecord and was returned back when became healthy

Documentation

• DNSPolicy Health Checks: https://docs.kuadrant.io/multicluster-gateway-controller/docs/dnspolicy/dns-health-checks/
• Endpoint removal MGC PR: Delete Endpoint from DNSRecord when endpoint it's related probe is marked with status healthy: false multicluster-gateway-controller#412

Additional context

Steps from the DNSPolicy Health Checks documentation after unhealthy endpoint was detected:

1. The health check probe identifies an endpoint as "unhealthy" and it’s got greater consecutive failures than failure threshold.
2. The system reacts by immediately removing the unhealthy endpoint from the list of available endpoints, any endpoint that doesn’t have at least 1 healthy child will also be removed.
3. This removal causes traffic to automatically get redirected to the remaining healthy endpoints.
4. The health check continues monitoring the endpoint's status. If it becomes healthy again, endpoint is added to the list of available endpoints.

Test cases

• Test for endpoint removal from available endpoints in DNSRecord and its return when becomes healthy

[martinhesko]

Putting this in the backlog for now due to the changes with DNS Health checks

For future reference: For an unhealthy health check to have an effect on DNSRecord there need to be some healthy endpoints, see Removing unhealthy Endpoints

[averevki]

Closed in favor of #572