Fluent2 datagrid cell style based on DefaultDataGridCellStyle

### Description

I want to adapt the .net 9 fluent theme's DefaultDataGridCellStyle so the grid cells do not look that cramped. Thus, I added a border and centered the cell's content:

```csharp

<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="DataGridCell">
<Border Padding="8" Background="{TemplateBinding Background}">
<ContentPresenter VerticalAlignment="Center" />
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>

```
Using that code, I override the default ControlTemplate completely and loose existing functionality. Instead I want to add those changes to the existing template. How can I achieve this? Or is there an overall better way?

I need the dark and the light theme to work as they are supposed to.

Thanks in advance.