Allow for labelling of the row headers.

Describe the new feature being added

Allow row headers to be editable.

How will this feature improve this extension

I often like to create spreadsheets with my own row labels and column labels. This format doesn't look nice on Excel or Google Sheets because you end up just using a portion of the body region to label rows and columns.

Describe alternatives you've considered

Optional multiple row (an column headers). I think this should be perhaps done as well.

Additional context
Column headers are already editable, which is a really nice feature!