Add style property to column definition

[josh-griffin]

Would like to be able to change the font size of the column headers. I thought a simplish way to do this might be to add a style prop to the ColumnDefinition.

Maybe something like

interface ColumnStyles {
    cellStyles: // Same object as `sx`?
    headerStyles: // Same object as `sx`?
}

It's also possible that we can just reduce the column header font sizes in general 🤔

[mark-prins]

There are other issues for font size realignment: #1149 #517
Will close this for now, haven't had the need for column style props yet.