generateRandom() does not support generating random Date32 value:

```
SELECT *
FROM generateRandom('Date32 Date32', NULL, 10, 2)
LIMIT 10

Received exception from server (version 21.11.5):
Code: 48. DB::Exception: Received from localhost:9000. DB::Exception: The 'GenerateRandom' is not implemented for type Date32: While executing GenerateRandom. (NOT_IMPLEMENTED)
```

{
            auto column = type->createColumn();
            auto & column_concrete = typeid_cast<ColumnDecimal<Decimal256> &>(*column);
            column_concrete.getData().resize(limit);
            fillBufferWithRandomData(reinterpret_cast<char *>(column_concrete.getData().data()), limit * sizeof(Decimal256), rng);
            return column;
        }
        case TypeIndex::FixedString:
        {
            size_t n = typeid_cast<const DataTypeFixedString &>(*type).getN();
            auto column = ColumnFixedString::create(n);
            column->getChars().resize(limit * n);
            fillBufferWithRandomData(reinterpret_cast<char *>(column->getChars().data()), limit * n, rng);
            return column;
        }
        case TypeIndex::DateTime64:
        {
            auto column = type->createColumn();
            auto & column_concrete = typeid_cast<ColumnDecimal<DateTime64> &>(*column);
            column_concrete.getData().resize(limit);
            UInt64 range = (1ULL << 32) * intExp10(typeid_cast<const DataTypeDateTime64 &>(*type).getScale());
            for (size_t i = 0; i < limit; ++i)
                column_concrete.getData()[i] = rng() % range;   
            return column;
        }
        default:
            throw Exception("The 'GenerateRandom' is not implemented for type " + type->getName(), ErrorCodes::NOT_IMPLEMENTED);
    }
}
class GenerateSource : public SourceWithProgress