allow null or undefined as a constraint parameter on arrays

[petern160]

for array types can we have a constraint parameter that allows undefined or null values while constraining it to accept the minimum and maximum items

e.g. @constraint(minItems: 1, maxItems: 15, allowUndefinedOrNull: true)

[Synthetic-Dev]

this should probably be default behaviour based on the field type e.g.:
field: [String!] allows field to be null
field: [String]! allows field items to be null (should nulls count towards the item count though?)