App service Hostname should use DNS suffix generated by DNL

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

Currently we generate App Service hostname using Resource Group ID, which is unique globally. The intent being that the hostname is also globally unique and predictable for resolving service dependencies.

But the platform uses DNL to ensure unique hostname and it is going to become default behavior in future. If enabled by default, it would break the current code.

### Describe the solution you'd like

We need to get the app service hostname that is generated with DNL.

### Additional context

_No response_