Upstream mode that combines responses

### 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

### Description

#### What problem are you trying to solve?

Finding the fastest IP address can be time-consuming, and due to network fluctuations, the IP address obtained through testing may not be the true fastest one.

I use a proxy tool called Surge that initiates TCP handshakes to all IP addresses for domains with multiple IPs simultaneously and selects the fastest connection for subsequent requests. This logic ensures that when accessing websites with a large number of balanced nodes, the fastest node in terms of response speed can always be used, and problematic nodes can be bypassed directly. This can save time for AdGuardHome to test the fastest IP address.

#### Proposed solution

AdGuardHome can query all DNS servers, merge all query results, and immediately return them without testing the fastest IP address.