Only write blocked request in query logs

### 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

I want to keep query logs to a minimum. Ideally, if a query is allowed, I don't really want logs of it at all (perhaps just stats).
But if I see some number in the "Blocked malware" - for example - I'd like for a way to investigate which client device made the query and what the query was to decide if I need to take further action.
Right now this is a all-or-nothing scenario where I either log everything or nothing.

### Proposed solution

Add an option to only log blocked requests.

### Alternatives considered and additional information

I considered middle grounds such as logging for a limited time frame and other such solutions as a compromise but they all hinder my ability to investigate the issues.