Make TLS certificates setup automatically

### What problem are you trying to solve?

Cloudflare Pages automatically re-scans DNS records and make the website available automatically after I setup DNS records.

Deno Deploy need me to click a button in dash.deno.com.

### Describe the solution you'd like

Let the user choose between automatic certs and custom certs (upload files) **before** DNS records are up.

If the user picked auto certs, Have the backend poll for DNS records continuously and setup automatic certs.

If the user picked custom certs, the `_acme-challenge` record isn't needed. Don't check for DNS records and serve the certs directly.

### Describe alternatives you've considered

N/A

### Documentation, Adoption, Migration Strategy

_No response_

The issue names no repository files, tests, or entry points. First identify the implementation repository and the existing certificate and DNS setup flow. Done means users choose automatic or custom certificates before DNS setup, automatic mode provisions after DNS becomes available, and custom mode bypasses _acme-challenge and serves uploaded certificates.

Written by the indexing model from the issue text.