fix(admin-delegation): display delegated section in common settings for non-admin

IDeclarativeSettingsForm can't be delegated and can be shown only to admin.
Lets not load IDeclarativeSettings for non admins.
Otherwise we get "Access forbidden" while displaying /settings/admin
and prevent to show delegated sections to non admin like:

Background jobs   OCA\Settings\Settings\Admin\Server
Email server      OCA\Settings\Settings\Admin\Mail

Signed-off-by: Misha M.-Kupriyanov <kupriyanov@strato.de>

Author: printminion-co

apps/settings/lib/Controller/CommonSettingsTrait.php

@@ -136,13 +136,17 @@ private function getIndexResponse(string $type, string $section): TemplateRespon
 		$user = $this->userSession->getUser();
 		assert($user !== null, 'No user logged in for settings');
 
-		$this->declarativeSettingsManager->loadSchemas();
-		$declarativeSettings = $this->declarativeSettingsManager->getFormsWithValues($user, $type, $section);
+		$declarativeSettings = [];
 
-		foreach ($declarativeSettings as &$form) {
-			foreach ($form['fields'] as &$field) {
-				if (isset($field['sensitive']) && $field['sensitive'] === true && !empty($field['value'])) {
-					$field['value'] = 'dummySecret';
+		if ($type !== 'admin' || $this->groupManager->isAdmin($user->getUID())) {
+			$this->declarativeSettingsManager->loadSchemas();
+			$declarativeSettings = $this->declarativeSettingsManager->getFormsWithValues($user, $type, $section);
+
+			foreach ($declarativeSettings as &$form) {
+				foreach ($form['fields'] as &$field) {
+					if (isset($field['sensitive']) && $field['sensitive'] === true && !empty($field['value'])) {
+						$field['value'] = 'dummySecret';
+					}
 				}
 			}
 		}