Add AWS Provider Health Checks

[mikenairn]

What

Add implementation of health checks for AWS provider.

How

We had AWS provider health checks in MGC but we removed them when we thought we weren't going forward with provider health checks Kuadrant/multicluster-gateway-controller@89e1893. This can be used for reference.

Areas to consider in this work:

• New health check is required if an IP / CNAME in spec doesn't have a matching status health check
• When a new health check is required
  • List health checks in Provider
  • Add all relevant health checks to DNS Record status
  • Create any absent health checks
  • Delete any obsolete health checks

## Overview

• Health check defined in DNS Policy.
• Health check config is propagated to the DNS Operator via the DNS Record spec (in same format as DNS Policy).
• When values are present in DNS Record and health checks are supported in the provider: health checks are created in provider for all A record targets or external CNAME targets.
• Health checks created with name including the owner ID (if present)
• Store health check IDs in status of the DNS Record
  • Hostname
  • IP / External CNAME
  • Health check ID
• Remove health checks for IPs / external CNAMEs in the status that are no longer in the endpoints.
  • If the health check delete fails because it's already gone, then remove it from the status.