OEL-450: Theme the site branding block.

Created by: abel-santos-corral

Add twig to override block--system-branding-block and add classes to it.

templates/overrides/navigation/block--system-branding-block.html.twig

+{% extends "block.html.twig" %}
+{#
+/**
+ * @file
+ * Theme override for a branding block.
+ *
+ * Each branding element variable (logo, name, slogan) is only available if
+ * enabled in the block configuration.
+ *
+ * Available variables:
+ * - site_logo: Logo for site as defined in Appearance or theme settings.
+ * - site_name: Name for site as defined in Site information settings.
+ * - site_slogan: Slogan for site as defined in Site information settings.
+ */
+#}
+{% block content %}
+  {% if site_logo %}
+    <a href="{{ path('<front>') }}" rel="home" class="site-logo">
+      <img src="{{ site_logo }}" alt="{{ 'Home'|t }}" />
+    </a>
+  {% endif %}
+  {% if site_name %}
+    <div class="site-name">
+      <a class="h1 text-white text-decoration-none align-bottom" href="{{ path('<front>') }}" rel="home">{{ site_name }}</a>
+    </div>
+  {% endif %}
+  {% if site_slogan %}
+    <div class="site-slogan">{{ site_slogan }}</div>
+  {% endif %}
+{% endblock %}