Add icons for the column headers within datagrid

[andrzejewsky]

Describe a proposed solution

We want to ged rid of grouped headers (eg. warehouses on variants grid) and for better visibility we can use icons that indicates what kind of data we have. For now we can use icons based on the rendered input type but later on we can use icons that depends on the resource type

Acceptance Criteria

• [ ] As a User I should see icon on each column, depending on represented input type
• [ ] As developer I should be able to override any icon
• [ ] As developer I should be able to set icon based on the resource type with fallback to default icon based on rendered input

[stale[bot]]

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