Get rid of Server.internalProxy

### 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?

The internal DNS client, `dnsforward.Server.internalProxy`, is used for a few tasks, such as resolving IP addresses during an autoupdate or resolving hostnames for runtime clients. There are two issues with this:

1. Not all upstream and similar settings are applied to it. See, for example, #4403.

2. These queries aren't logged into the query log.

#### Proposed solution

Remove it and use the same DNS client that we use for forwarding. Mark these queries as “internal” or something like that in the Query Log.

#### Alternatives considered

Configure the internal proxy the same way as the main one. This increases code duplication and complicates data flow.

@ameshkov, what do you think?