Repeated customtype fields generate slices w/o pointer to the custom type

[maros7]

As I mentioned in #477, a Protobuf message containing a repeated field with the customtype option set does not generate a slice of pointers.

Another observation related to customtype is that it doesn't generate a slice of pointers for repeated customtype fields. repeated common.BigDecimal repeated_big_decimal_value = 37 [(gogoproto.customtype) = "go-decimal/pbdecimal.Decimal"]; generates RepeatedBigDecimalValue []go_decimal_pbdecimal.Decimal. I expected RepeatedBigDecimalValue []*go_decimal_pbdecimal.Decimal But I can open a separate issue for this matter.

[Nagaraj007]

I am also facing same issue, Any updates on creating the slice pointer using customtype, i have created
#496