Identify alternative solutions for monitoring 3scale portals

It is my understanding that RHOAM does not currently support custom domains for the admin or master portals due to the way the alerting is setup.

This is a request to add support for this by modifying the existing alerting and service definitions and agreements.

One proposed solution would be to break the alert into two parts and calling the OCP router directly without the use of DNS.
For example:

Primary Alert - Error if this fails: `curl -k https://<custom-domain> --resolve <custom-domain>:443:<ocp router ip>`
Secondary Alert - Warning if this fails: `curl https://<custom-domain>`

In the event that the warning occurs we can provide the primary alert command as proof that the service is responding at the appropriate IP addresses that the customer's DNS should be configured for. The warning will indicate that the customer needs to verify the DNS and certificate on their end and this warning would be independent of any SLAs.

If we do support custom domains we have to presume that some customers will want to change the domain after installation. This would require implementing THREESCALE-1096 on the 3scale side to avoid any requests for SRE to make changes manually in the rails console. Changing the developer portal and apicast IS already supported: MGDAPI-3899, however the alerting still needs to be changed to be fully supported.