Support the use of custom domains in RHOAM

On-prem users can configure custom domains for the different 3scale components. There are ways to achieve it also in RHOAM but, when customers do this, it causes issues because the SRE team can only monitor and provide SLO for the default domains.

The aks is to allow configuring additional hosts as aliases for the Developer Portal, the API Gateways(APIcast), and the Admin Portal while keeping the default domains operational. This way, RHOAM team will be able to preserve monitoring and alerting.