Convert explore tabs to pajamas

Changelog: other

app/views/explore/groups/_nav.html.haml

 .top-area
-  %ul.nav-links.nav.nav-tabs
-    = nav_link(page: explore_groups_path) do
-      = link_to explore_groups_path do
-        = _("Explore Groups")
+  = gl_tabs_nav({ class: 'gl-display-flex gl-flex-grow-1 gl-border-none'}) do
+    = gl_tab_link_to _("Explore Groups"), explore_groups_path
   .nav-controls
     = render 'shared/groups/search_form'
     = render 'shared/groups/dropdown'