support ECN change for DNS Rewrites

### Prerequisites

- [x] I have checked the [Wiki](https://github.com/AdguardTeam/AdGuardHome/wiki) and [Discussions](https://github.com/AdguardTeam/AdGuardHome/discussions) and found no answer

- [x] I have searched other issues and found no duplicates

- [x] I want to request a feature or enhancement and not ask a question

### The problem

In today’s challenging world, there is a problem where entire countries and networks are blocked via EDNS.
This means we have to set up separate virtual DNS servers with ECS spoofing.

### Proposed solution

Currently, you can specify a global ECN (Use custom IP for EDNS) for upstreams. However, it would be great if you could specify a rewrite rule to substitue the specified ECN for domain.

### Alternatives considered and additional information

_No response_