Support forwarding for CNAMEs

Hello 👋

Currently, upstreams for specific domains are limited to explicit domain names only.

It would be very helpful if CNAMEs could be forwarded too.

Unbound supports this with `forward-zone`, pdns-rec with `forward-zones-recurse`... where the FQDN in the DNS chain is resolved with the specified server.

### Current design

Let's say I want to forward all `*.akamai.net` queries to a specific resolver, I'm limited to the following:

```text
[/akamai.net/]8.8.8.8
```

E.g. `a1802.dscb.akamai.net` will be forwarded if queried directly, however `se2.itunes.apple.com` will not be.

```text
❯ kdig +short +tls @1.1.1.1 se2.itunes.apple.com
se2-cdn.itunes-apple.com.akadns.net.
se2.itunes.apple.com.edgesuite.net.
a1802.dscb.akamai.net.
23.210.245.112
23.210.245.80
```

My ISP's DNS servers return responses for servers that are located closer to me. While ECS works great, it's not enough.

**EDIT/2**: clarify feature request