fix(search): Add alternative text to images and lazy load them

The alternative text used is "SONG by ARTISTS", where SONG and ARTISTS
are placeholders for their relevant properties.

Lazy loading attribute must be placed currently as the first one of img
elements for Firefox, see
https://bugzilla.mozilla.org/show_bug.cgi?id=1647077.

templates/search/search.html.twig

@@ -12,14 +12,16 @@
     <h1>results for {{ query }}! ✅</h1>
     {% for result in results %}
         {% set array = result['title']|split('-') %}
+        {% set artist = array[0] %}
+        {% set song = array[1] %}
         <div>
             <div>
-                artist : {{array[0]}}
+                artist : {{artist}}
             </div>
             <div>
-                song : {{array[1]}}
+                song : {{song}}
             </div>
-            <img src={{result['cover_image']}}></img>
+            <img loading="lazy" src={{result['cover_image']}} alt="{{song ~ ' by ' ~ artist}}" />
         </div>
     {% endfor %}
     <a href="/search?q={{query}}&page={{previous_page}}">previous page</a>