fe_comment: Feedback Overview content element in the page JSON

- New content element "Feedback Overview" (CType fecomment_overview):
  the current FE user's feedback state under content.feedbackOverview,
  so the overview page renders like any other page instead of a
  front-end special case
- Rendered as USER_INT inside the cached page JSON (EXT:headless replaces
  the field per request): data is per user, visitors without a session
  get {"allowed": false} - verified that nothing leaks from the cache
- One implementation for both consumers: the new FeedbackState service
  builds the state payload; the API middleware delegates to it
- State payload (API and element) gained canSubmit and actions (all
  write endpoints with method and URL), so the front end needs no
  hard-coded endpoints for the submit button below the ticket list
- New site set evomedien/fe-comment carries the TypoScript, added to the
  site configuration; icon fecomment-overview

packages/fe_comment/Configuration/Icons.php

@@ -0,0 +1,8 @@
+<?php
+
+return [
+    'fecomment-overview' => [
+        'provider' => \TYPO3\CMS\Core\Imaging\IconProvider\SvgIconProvider::class,
+        'source' => 'EXT:fe_comment/Resources/Public/Icons/Extension.svg',
+    ],
+];