This commit makes it so the site settings filter controls and
the list of settings input editors themselves can be used elsewhere
in the admin UI outside of /admin/site_settings
This allows us to provide more targeted groups of settings in different
UI areas where it makes sense to provide them, such as on plugin pages.
You could open a single page for a plugin where you can see information
about that plugin, change settings, and configure it with custom UIs
in the one place.
In future we will do this in "config areas" for other parts of the
admin UI.
Why this change?
Prior to this change, there is no description being displayed for
objects typed theme setting because we were rendering a button instead
of the components for the various setting types which will render the
setting's description.
What does this change do?
1. Introduce `SiteSettings::Description` compoment to centralise the HTML
being rendered across all settings component.
2. Renders the `SiteSettings::Description` component after the edit
button in `site_setting.hbs`.
Why this change?
The `/admin/customize/themes/:id/schema/name` route is a work in
progress but we want to be able to start navigating to it from the
`/admin/customize/themes/:id` route.
What does this change do?
1. Move `adminCustomizeThemes.schema` to a child route of
`adminCustomizeThemes.show`. This is because we need the model
from the parent route and if it isn't a child route we end up
having to load the theme model again from the server.
1. Add the `objects_schema` attribute to `ThemeSettingsSerializer`
1. Refactor `SiteSettingComponent` to be able to render a button
so that we don't have to hardcode the button rendering into the
`SiteSettings::String` component
