Move pfSense from ISC DHCP to Kea DHCP

ISC DHCP is deprecated in pfSense now, and when Kea DHCP was first introduced, well, there were a lot of issues and bugs. And since ISC DHCP was not going anywhere soon, I decided to wait before making the switch. Now I feel like the Kea DHCP is on par with ISC, and I can safely make the switch. Here is how I do it.