Represent long with logicalType timestamp-millis as time.Time

[gubtos]

I use hamba/avro as avro and after last update (https://github.com/hamba/avro/pull/368) the unmarshal was resulting error the following error to me.

Timestamp: avro: int64 is unsupported for Avro long and logicalType timestamp-millis

I use the following avro definition

"type": {
                "type": "long",
                "logicalType": "timestamp-millis"
            },

If the logicalType was timestamp-*, wouldn't it be better map to time.Time ?