This commit finalises the admin setting page consistency
efforts by:
* Converting all route templates into .gjs
* Adding `@hideTabs={{true}}` for all the page headers so we
don't show a border line when it's not needed
* Introduce `@showBreadcrumb` and default to true for
AdminAreaSettings, for all these pages the Settings part of
the breadcrumb is redundant
* UX: Admin setting page consistency - Group permissions (#30528)
Followup c2282439b3 and
21470e4afd
Adds a new "Group permissions" page and group_permissions site
setting area, which shows every single group-based site setting
in the app and core plugins.
Also adds a "trust_levels" area to show on the already moved
admin "Trust level" settings page, since that previously was
showing a mix of trust level settings and allowed group settings.
* DEV: Review fixes
