Customer request: relax constraints on allowable option types to permit option type 0 (and 255?)

We have a customer who would like us to relax the constraints on option types which forbid using an option with code 0, which is apparently permissible in ISC DHCP and used by one of their network equipment vendors.

When they try to configure such an option in Kea they get:

2019-03-28 11:23:01.204 ERROR [kea-dhcp4.dhcp4/3841] DHCP4_PARSER_FAIL failed to create
or run parser for configuration element client-classes: option data does not match option
definition (space: ZTP, code: 0): Can't create V4 option of type 0, V4 options are in
range 1..254 (/etc/kea/kea-dhcp4.conf:144:33)

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