Add table header information to match IDE's table output

[dcossyleon]

Table output from an RMarkdown code chunk in the IDE includes header information, e.g. to show grouped output:

The current paged table output in learnr does not include this information.

Adding table header information to match the IDE's table output would make it easier to teach and learn about topics like groupings and tibble formatting, without needing switch to default "console style" printing and forgo the UX benefits of paged interactive output.

[garrettgman]

+ 1