The new site setting `allow_anonymous_and_tl0_to_flag_illegal` allows
tl0 users to flag illegal content. In addition, anonymous users are
instructed on how to flag illegal content by sending emails.
Also `email_address_to_report_illegal_content` setting is added. If not
provided, then the site contact email is used.
A new setting attribute is used to define the areas (separated by `|`).
In addition, endpoint `/admin/config/site_settings.json` accepts new `filter_area` data.
Followup 4aea12fdcb21216a528451c0f8803e02dff24998
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.
