Enable Word Auto-Pagination Using Group Variable

This function uses the applies the functionality flextable::keep_with_next() by automatically building the row indices using some grouping variable. Each group identified by the variable (i.e. when the value of the variable changes) will be set as a "keep_with_next" group in Word. Using this functionality, Word will attempt not to break that group across pages, enabling smoother pagination without having to do specific calculations of page breaks.