**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 auto & partition_ast = ast->as<ASTPartition &>();
    if (!partition_ast.value)
        return partition_ast.id;
    if (format_version < MERGE_TREE_DATA_MIN_FORMAT_VERSION_WITH_CUSTOM_PARTITIONING)
    {
        
        const auto * partition_lit = partition_ast.value->as<ASTLiteral>();
        if (partition_lit && partition_lit->value.getType() == Field::Types::String)
        {
            String partition_id = partition_lit->value.get<String>();
            if (partition_id.size() != 6 || !std::all_of(partition_id.begin(), partition_id.end(), isNumericASCII))
                throw Exception(
                    "Invalid partition format: " + partition_id + ". Partition should consist of 6 digits: YYYYMM",
                    ErrorCodes::INVALID_PARTITION_VALUE);
            return partition_id;
        }
    }
    
    auto metadata_snapshot = getInMemoryMetadataPtr();
    size_t fields_count = metadata_snapshot->getPartitionKey().sample_block.columns();
    if (partition_ast.fields_count != fields_count)
        throw Exception(
            "Wrong number of fields in the partition expression: " + toString(partition_ast.fields_count) +