feat: add schema.org json-ld objects to podcasts, episodes, posts and comments pages

- refactor meta-tags by generating them in the controller and injecting them into the views
- use
`melbahja/seo` library to build opengraph and twitter meta-tags + schema.org objects

app/Controllers/MapController.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright  2020 Podlibre
+ * @license    https://www.gnu.org/licenses/agpl-3.0.en.html AGPL3
+ * @link       https://castopod.org/
+ */
+
+namespace App\Controllers;
+
+use App\Models\EpisodeModel;
+use CodeIgniter\HTTP\ResponseInterface;
+
+class MapController extends BaseController
+{
+    public function index(): string
+    {
+        $locale = service('request')
+            ->getLocale();
+        $cacheName = "page_map_{$locale}";
+        if (! ($found = cache($cacheName))) {
+            $found = view('pages/map', [], [
+                'cache' => DECADE,
+                'cache_name' => $cacheName,
+            ]);
+        }
+        return $found;
+    }
+
+    public function getEpisodesMarkers(): ResponseInterface
+    {
+        $cacheName = 'episodes_markers';
+        if (! ($found = cache($cacheName))) {
+            $episodes = (new EpisodeModel())
+                ->where('`published_at` <= NOW()', null, false)
+                ->where('location_geo is not', null)
+                ->findAll();
+            $found = [];
+            foreach ($episodes as $episode) {
+                $found[] = [
+                    'latitude' => $episode->location->latitude,
+                    'longitude' => $episode->location->longitude,
+                    'location_name' => $episode->location->name,
+                    'location_url' => $episode->location->url,
+                    'episode_link' => $episode->link,
+                    'podcast_link' => $episode->podcast->link,
+                    'cover_path' => $episode->cover->thumbnail_url,
+                    'podcast_title' => $episode->podcast->title,
+                    'episode_title' => $episode->title,
+                ];
+            }
+            // The page cache is set to a decade so it is deleted manually upon episode update
+            cache()
+                ->save($cacheName, $found, DECADE);
+        }
+        return $this->response->setJSON($found);
+    }
+}