Add support for custom DNS servers

## Description

Allow users to specify custom DNS servers for the hotspot.

## Desired behavior
\\\ash
nm-hotspot create -s MyNet -p Pass123 --dns 8.8.8.8,8.8.4.4
\\\

## Implementation hints
- Modify NetworkManager connection settings
- Use \
mcli connection modify\ to set DNS servers
- Support both IPv4 and IPv6 DNS

## Difficulty
Medium