Option to import clients from file

### Description

#### What problem are you trying to solve?
To write docker container's name instead of ip

#### Proposed solution
To have option to pass client - ip list to adguardhome (like simple "ip- name"). Adguardhome already read content of /etc/hosts, it would be nice to have option to just specify custom path to "hosts" file

And then something simple like ` docker ps -q | xargs -n 1 docker inspect --format '{{range .NetworkSettings.Networks}} {{.IPAddress}}{{end}} {{ .Name }} ' | tr -d '/' > /tmp/adguardhome_clients_list` by cron

#### Alternatives considered
- change system's /etc/hosts by cron
- Running dnsmasq for serving ptr records
- ??