meson: docs: Allow configuring simple/website style
The meson docs generation hardcoded using the website style so far. Make it
configurable via a meson option.
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Reported-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/
3fc3bb9b-f7f8-d442-35c1-
ec82280c564a@enterprisedb.com