import of dnsmasq dhcp.conf file for easier migration

### 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

As dnsmasq is a widely spread software package for small local dns and dhcp I think AGH would benefit from an easy migration. (I currently have ~40 static entries).

### Proposed solution

Provide an import option on the UI which parses dnsmasq's dhcp.conf file for ranges, dhcp-host & srv-host entries and comments.

### Alternatives considered and additional information

Provide some supporting tool to update config in AdGuardHome.yaml and leases.json.