[AIRFLOW-5658] Fix broken navigation links (#6374)

Configuration and Version links are broken when running airflow
behind reverse proxy.

Registering navigation links through their respective views
ensure that correct links are rendered in the menu.

(cherry picked from commit e77fa1ac5e6f02b6ee7d9dc8465c7e3a67eddba5)
diff --git a/airflow/www_rbac/app.py b/airflow/www_rbac/app.py
index a47e2ce..3a62c0f 100644
--- a/airflow/www_rbac/app.py
+++ b/airflow/www_rbac/app.py
@@ -106,8 +106,6 @@
             from airflow.www_rbac import views
             appbuilder.add_view_no_menu(views.Airflow())
             appbuilder.add_view_no_menu(views.DagModelView())
-            appbuilder.add_view_no_menu(views.ConfigurationView())
-            appbuilder.add_view_no_menu(views.VersionView())
             appbuilder.add_view(views.DagRunModelView,
                                 "DAG Runs",
                                 category="Browse",
@@ -124,8 +122,8 @@
             appbuilder.add_view(views.TaskInstanceModelView,
                                 "Task Instances",
                                 category="Browse")
-            appbuilder.add_link("Configurations",
-                                href='/configuration',
+            appbuilder.add_view(views.ConfigurationView,
+                                "Configurations",
                                 category="Admin",
                                 category_icon="fa-user")
             appbuilder.add_view(views.ConnectionModelView,
@@ -147,8 +145,8 @@
             appbuilder.add_link("GitHub",
                                 href='https://github.com/apache/airflow',
                                 category="Docs")
-            appbuilder.add_link('Version',
-                                href='/version',
+            appbuilder.add_view(views.VersionView,
+                                'Version',
                                 category='About',
                                 category_icon='fa-th')
 
diff --git a/airflow/www_rbac/views.py b/airflow/www_rbac/views.py
index dabe41e..5dfb266 100644
--- a/airflow/www_rbac/views.py
+++ b/airflow/www_rbac/views.py
@@ -1913,6 +1913,8 @@
 
 
 class VersionView(AirflowBaseView):
+    default_view = 'version'
+
     @expose('/version')
     @has_access
     def version(self):
@@ -1941,6 +1943,8 @@
 
 
 class ConfigurationView(AirflowBaseView):
+    default_view = 'conf'
+
     @expose('/configuration')
     @has_access
     def conf(self):