Upgrade to fontawesome 6

* Adapt fontawesome usage when needed
* Fix uv guide not importing css
* Remove utf8 usage for fontawesome

eboutic/templates/eboutic/eboutic_main.jinja

@@ -112,7 +112,7 @@
                       <img class="product-image" src="{{ p.icon.url }}"
                            alt="image de {{ p.name }}">
                     {% else %}
-                      <i class="fa fa-2x fa-picture-o product-image"></i>
+                      <i class="fa-regular fa-image fa-2x product-image"></i>
                     {% endif %}
                     <div class="product-description">
                       <h4>{{ p.name }}</h4>