Add backchannel logout, per application logout.

app/controllers/admin/applications_controller.rb

@@ -100,6 +100,7 @@ module Admin
       params.require(:application).permit(
         :name, :slug, :app_type, :active, :redirect_uris, :description, :metadata,
         :domain_pattern, :landing_url, :access_token_ttl, :refresh_token_ttl, :id_token_ttl,
+        :icon, :backchannel_logout_uri,
         headers_config: {}
       ).tap do |whitelisted|
         # Remove client_secret from params if present (shouldn't be updated via form)