Be able to skip caching when using fallback DNS

### 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

Right now, no matter where the DNS response gets, it will be cached (if enabled) by AdGuard Home. I wonder whether it's possible to not record the response from fallback DNS to the cache.

### Proposed solution

Maybe add an option to skip caching when using fallback DNS.

### Alternatives considered and additional information

_No response_