Add slots for mt-data-table

[quando1910]

Package
@meteor/component-library

Description
The current mt-data-table does not support slots for some places we want to customize:

• Customize cell of mt-data-table. For example: with product name column, we want to show the product name and the variant below in the same column and style for it.

• Change the edit button to another action.

• Customize the filter button. It will open a modal instead of the popover.

• Customize the menu item in context button

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