Should network-instance type be mandatory?

[dplore]

network-instance type is currently optional and has no default. When configuring a network instance, it is currently ambiguous as to which type a network operating system (NOS) will use.

It seems network-instance type should be mandatory in order to get deterministic behavior. Modifying the current leaf would be a breaking change.

Model Reference: https://github.com/openconfig/public/blob/f3f05d5f6e38ca7c46671ea5a4c11b62d264c10b/release/models/network-instance/openconfig-network-instance.yang#L1193-L1208

featureprofiles test which exposed this issue: https://github.com/openconfig/featureprofiles/pull/624