Followup 4aea12fdcb
In certain config areas (like About) we want to be able
to fetch specific site settings by name. In this case,
sometimes we need to be able to fetch hidden settings,
in cases where a config area is still experimental.
Splitting out a different endpoint for this purpose
allows us to be stricter with what we return for config
areas without affecting the main site settings UI, revealing
hidden settings before they are ready.
This commit continues work laid out by ffec8163b0 for the admin config page for the /about page. The last commit set up the user interface, and this one sets up all the wiring needed to make the input fields and save buttons actually work.
Internal topic: t/128544.
