feat(nimbus): add documentation links to new nimbus ui

Because

* We need to show the documentation links in the left sidebar
* We want to show the new header with the title and timeline on every page

This commit

* Adds documentation links to the sidebar
* Improves the styling of the sidebar
* Moves the new header to the base template so it appears on all pages

fixes #11924

experimenter/experimenter/nimbus_ui_new/static/css/style.scss

@@ -118,3 +118,7 @@
     }
   }
 }
+
+.nav-link-hover:hover {
+  background-color: var(--bs-secondary-bg);
+}

experimenter/experimenter/nimbus_ui_new/templates/common/sidebar_link.html

@@ -1,7 +1,6 @@
-<li class="nav-item fw-semibold">
-  <a href="{{ link }}"
-     class="nav-link {% if disabled %}disabled{% endif %}">
-    <i class="{{ icon }}"></i>
-    <span>{{ title }}</span>
-  </a>
-</li>
+<a {% if external %}target="_blank"{% endif %}
+   class="nav-link mb-2 {% if request.path == link %}active{% endif %} nav-link-hover {% if disabled %}disabled{% endif %}"
+   href="{{ link }}">
+  <i class="{{ icon }} col-2"></i>
+  {{ title }}
+</a>

experimenter/experimenter/nimbus_ui_new/templates/common/with_sidebar.html

@@ -26,6 +26,8 @@ <h5 class="offcanvas-title" id="offcanvasSidebarLabel">Filter</h5>
         </div>
       </div>
       <div class="col-xl-10 col-xxl-10">
+        {% block main_content_header %}{% endblock %}
+
         {% block main_content %}
         {% endblock main_content %}