Highlights:
- Reduced all DHCP events into a single dhcp_message event. (removed legacy events since they weren't widely used anyway)
- Support many more DHCP options.
- DHCP log is completely reworked and now represents DHCP sessions
based on the transaction ID (and works on clusters).
- Removed the known-devices-and-hostnames script since it's generally
less relevant now with the updated log.