Using MAC address for clients without enabling DHCP server

### Problem Description
Currently, Clients can only be identified by MAC address if AdGuard Home is also a DHCP server.
This is a significant limitation given the newness of limited capability of AGH DHCP server currently.

### Proposed Solution
As the client MAC will be in the network packets, why can't MAC address identifiers be used even if AGH is not the DHCP server? Requiring that AGH be the DHCP server significantly limits the abilty to use client filters and this would likely impact the vast majority of AGH users.

### Alternatives Considered
Do not wish to use AGH DHCP server at this time due to features missing that are available in more mature DHCP servers.
AGH DHCP Server is still considered "Experimental" (it is labeled this way in the UI)