[Bug]: No way to set DNS records with Deno Deploy without setting up a custom domain

### Problem description

Is there a way to set DNS records with Deno Deploy without setting up a custom domain? I'm not seeing one.

The context is that I want to use [Resend](https://resend.com/overview) to send emails to users to allow them to reset their password. In order to get set up with Resend, you need to set a few DNS records. I have my app all set up with Deno Deploy, but I'm not seeing a way to set the DNS records.

### Steps to reproduce

1. Deploy an app on Deno Deploy without a custom domain.
2. Try to set up DNS records.

### Expected behavior

A way to set up DNS records.

### Environment

_No response_

### Possible solution

_No response_

### Additional context

I'm cross posting here ([original post](https://github.com/denoland/deno/discussions/22401)) based on the advice in [this comment](https://github.com/denoland/deno/discussions/22401#discussioncomment-8507820).