dhcp: T3316: add deprecation warning on RAW ISC DHCPD options
The following CLI nodes are deprecated and will be remove in VyOS 1.5 while
moving to KEA as DHCP server.
- set service dhcp-server global-parameters
- set service dhcp-server shared-network-name <name> shared-network-parameters
- set service dhcp-server shared-network-name <name> subnet <x.x.x.x/y> subnet-parameters
Please open feature requests if any DHCP option is missing and should be added
as a proper CLI node to make your life easier.