**Describe the bug**

I have a table like:

```
CREATE TABLE test (
    time DateTime64(3)
    ...
) ENGINE = MergeTree()
PARTITION BY toStartOfInterval(time, INTERVAL 1 HOUR)
...
```

But when I search in `system.parts` it does not appear to have the `min/max` columns appropriately set?

```
partition:                             2020-06-01 01:00:00
min_date:                              1970-01-01
max_date:                              1970-01-01
min_time:                              1970-01-01 00:00:00
max_time:                              1970-01-01 00:00:00
```

I assume that if these were correctly set, doing a `select toStartOfInterval(time, interval 1 day), count()` type query would be pretty instant rather than trying to scan everything? I am guessing this is due to the `DateTime64` type in use?

Clickhouse 20.11.3.3

{"path",                                       std::make_shared<DataTypeString>()},
        {"column",                                     std::make_shared<DataTypeString>()},
        {"type",                                       std::make_shared<DataTypeString>()},
        {"column_position",                            std::make_shared<DataTypeUInt64>()},
        {"default_kind",                               std::make_shared<DataTypeString>()},
        {"default_expression",                         std::make_shared<DataTypeString>()},
        {"column_bytes_on_disk",                       std::make_shared<DataTypeUInt64>()},
        {"column_data_compressed_bytes",               std::make_shared<DataTypeUInt64>()},
        {"column_data_uncompressed_bytes",             std::make_shared<DataTypeUInt64>()},
        {"column_marks_bytes",                         std::make_shared<DataTypeUInt64>()}
    }
    )
{
}
void StorageSystemPartsColumns::processNextStorage(
    MutableColumns & columns, std::vector<UInt8> & columns_mask, const StoragesInfo & info, bool has_state_column)
{
    
    struct ColumnInfo
    {
        String default_kind;
        String default_expression;
    };
    std::unordered_map<String, ColumnInfo> columns_info;
    for (const auto & column : info.storage->getInMemoryMetadataPtr()->getColumns())
    {
        ColumnInfo column_info;
        if (column.default_desc.expression)
        {
            column_info.default_kind = toString(column.default_desc.kind);