Reservations with only a hardware address should be considered valid reservations

This configuration:

"reservations": [
  {
    "hw-address": "00:0c:01:02:03:04" 
  }
]

emits an error similar to: ERROR [kea-dhcp4.dhcp4/3274.281473783189520] DHCP4_PARSER_FAIL failed to create or run parser for configuration element shared-networks: specified reservation for DUID: hwtype=1 00:0c:01:02:03:04 must include at least one resource, i.e. hostname, IPv4 address, IPv6 address/prefix, options (kea-dhcp4.conf:19:26)

However, such a configuration would be advantageous to have in the case of a configuration similar to this:

"subnet4": [
  {
    "subnet": "192.0.2.0/24",
    "pools": [
      {
        "client-class": "KNOWN",
        "pool": "192.0.2.5 - 192.0.2.10"
      }
    ],
    "reservations": [
      {
        "hw-address": "00:0c:01:02:03:04" 
      }
    ]
  }
]

such that clients could be easily added to the KNOWN client-class without having the complexity of adding the client to some class or having to configure undesired options in the reservation.

RT 21642