Feature request: Make the DMARC check to be enforced regardless of DMARC record existence

I would like to propose a feature request for Maddy: the ability to customize behavior of DMARC checking.
Perhaps with this directive example:

```
check.dmarc {
none_action ignore | quarantine | reject
}
```

_none_action_ will override the DMARC check behavior for any sender domain that has no DMARC record, in turn allowing SPF check & DKIM check to verify the incoming email and will do action as configured when neither SPF nor DKIM passed the checks. For now the default value is _ignore_

This would allow us to follow the best practices of email security and deliverability, as recommended by Gmail, Yahoo Mail and other major mail providers ([https://www.valimail.com/blog/the-new-requirements-for-email-delivery-at-gmail/)](https://www.valimail.com/blog/the-new-requirements-for-email-delivery-at-gmail/)).

They have recently made DMARC mandatory (starting in April 2024) which helps prevent spoofing and phishing attacks. By allowing users to opt-in to DMARC checks enforcement, we can increase the trust and reputation of our email service, as well as protect our users from malicious emails.

- [ ] I'm willing to help with the implementation