Find a better way to display dataset extracts

[rossfarrugia]

We used head(adxxx, n=10) calls in the ADSL example so you can see the ADaM being built up at each step.

@bms63 had the comment: I'm sort of interested in using reactable or DT to render the tables - the outputs look a little sad right now :(

admiral vignettes use their own admiraldev::dataset_vignette() function but its a little heavier and sometimes can make pages slow to load, which is why Christina went with head() function from memory when first drafting the ADSL example.