Add CAP_NET_ADMIN to systemd unit

### 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

The user has to manually edit `/etc/sysctl.conf` values to get rid of the quic-go warning and benefit from improved QUIC performance.

### Proposed solution

quic-go v0.35.0+ uses `SO_RCVBUFFORCE` and `SO_SNDBUFFORCE` which doesn't require tinkering with sysctl limits. The only downside is that the process must be executed with the `CAP_NET_ADMIN` capability to do this.

Adding the following line to the systemd unit should fix this:

```
AmbientCapabilities=CAP_NET_ADMIN
```

### Alternatives considered and additional information

_No response_