In `summary_rows()`, allow for setting a key and a label

[rich-iannone]

[meghannash8]

This is so we can access the label for styling with tab_style? If so, yes, this is really needed. Could a key be set by default? Like, even if the user didn't explicitly add a label? I guess then we would have to be told what the autoset label is but it's better than nothing.