Add PUSH and POP operations for enums and custom scalars

[Andy2003]

I suggest to add PUSH and POP operations to array fields of custom scalars and enums.

Schema:

scalar CustomScalar
enum E {
   foo, bar
}

type Movie {
  id: ID
  customScalar: [CustomScalar!]
  enumField: [E!]
}

should generate

input MovieUpdateInput {
  customScalar: [CustomScalar!]
  customScalar_POP: Int
  customScalar_PUSH: [CustomScalar!]
  enumField: [E!]
  enumField_POP: Int
  enumField_PUSH: [E!]
  id: ID
}