### Bug report

When the Grid uses an external DataSource, the aggregates are undefined within the ClientGroupFooterTemplate().

### Reproduction of the problem

Use the following REPL sample that demonstrates the issue:

https://netcorerepl.telerik.com/mIkyQnvB382bsiFt24

1. Group the Grid by the "Freight" column.

2. An error is thrown in the browser console: "Uncaught ReferenceError: sum is not defined".

3. The aggregates=["sum"] is missing in the column options in the Grid initialization script;

"columns":[{"title":"Order ID","field":"OrderID","filterable":false,"encoded":true},{"title":"Freight","groupFooterTemplate":"Sum: #=sum#","field":"Freight","filterable":{"messages":{"title":"Show items with value that"},"checkAll":false},"encoded":true},{"title":"Ship City","width":"150px","field":"ShipCity","filterable":{"messages":{"title":"Show items with value that"},"checkAll":false},"encoded":true}]

When the DataSource is defined within the Grid configuration, the aggregate is displayed as expected.

### Expected/desired behavior

The "sum" aggregate must be displayed within the group footer template of the column when the Grid is grouped.

### Workaround

Define the DataSource in the Grid configuration or update the Grid settings by using the setOptions() method when the page is loaded:

<script>
    $(document).ready(function () {
        var grid = $("#grid").data("kendoGrid");
        if (grid) {
            let gridColumns = grid.columns;
            if (!gridColumns[1].aggregates) { // update [1] with the index of the column that has a group footer template. For example, "1" is the 2nd Grid column
                gridColumns[1].aggregates = ["sum"];
                grid.setOptions({ columns: gridColumns });
            }
        }
    });
</script>

### Environment

* **Telerik UI for ASP.NET Core/MVC: 2024.1.319
* **Browser: [all]

### Bug report

When there is an initially hidden column in the Grid with multi-column headers, the hiding/showing of columns through the ColumnMenu does not work correctly.

### Reproduction of the problem

1) Hide a column in the Grid with the Hidden(true) option.

2) Hide a column through the Grid column menu.

3) The header of the column that is hidden is added to the previous visible column.

4) Show the same column through the column menu - it does not render back as expected.

The issue is caused by the a mismatch in the column group header rendering:

• Group header:
  • aria-haspopup="dialog" is missing;
  • data-title="{group name}" is missing;
  • the title in the group header must be rendered as:

<span class="k-cell-inner"><span class="k-link"><span class="k-column-title">Product Information</span></span></span>

• Header:
  • aria-haspopup="menu" is missing;

### Environment

* **Telerik UI for ASP.NET MVC version 2024.2.514