Drop all invalid requests.

### Problem Description

I found that some clients send some weird requests like this:

```
Query: NS org/saveWb.json? -> RCodeNameError
Query: NS bdimg.com443443 -> RcodeNameError
Query: NS 28.152 -> RCodeNameError
Query: NS http://ww114.18 -> RCodeNameError
...
```

There is no doubt that these requests will not be answered in any meaningful way.

### Proposed Solution

I think we might be able to allow AdGuardHome to drop all invalid requests. **This avoids sending many invalid requests to the upstream, and make AdGuardHome's average processing time unaffected by invalid requests.** Hope to hear your opinions and hope my suggestion is helpful.

### Additional Information

We might also make this optional, allowing some users to customize any kind of record on their internal network.