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
Async, modern syntax, no `on()` component hooks, const extraction, sorted props, template tweaks, and a small filtering bugfix (filtering could throw errors after saving a category-selection setting)
