**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

const String & name, const VolumePtr & volume, const String & relative_path) const
{
    return createPart(name, MergeTreePartInfo::fromPartName(name, format_version), volume, relative_path);
}
MergeTreeData::MutableDataPartPtr MergeTreeData::createPart(
    const String & name, const MergeTreePartInfo & part_info,
    const VolumePtr & volume, const String & relative_path) const
{
    MergeTreeDataPartType type;
    auto full_path = relative_data_path + relative_path + "/";
    auto mrk_ext = MergeTreeIndexGranularityInfo::getMarksExtensionFromFilesystem(volume->getDisk(), full_path);
    if (mrk_ext)
        type = getPartTypeFromMarkExtension(*mrk_ext);
    else
    {
        
        type = choosePartTypeOnDisk(0, 0);
    }
    return createPart(name, type, part_info, volume, relative_path);
}
void MergeTreeData::changeSettings(