rssbridge: Use OpenID Connect instead of pubtkt based SSO

Tests:

- Functional tests work.

- Admin user is able to access the application

- User belonging to special group is able to access the application

- Regular user is not able to access the application

- Anonymous user is not able to access the application

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/rssbridge/data/usr/share/freedombox/etc/apache2/conf-available/rss-bridge.conf

@@ -15,10 +15,8 @@ Alias /rss-bridge /usr/share/rss-bridge
         </If>
         <Else>
             # Formats: Html and all other pages
-            Include includes/freedombox-single-sign-on.conf
-            <IfModule mod_auth_pubtkt.c>
-                TKTAuthToken "feed-reader" "admin"
-            </IfModule>
+            Use AuthOpenIDConnect
+            Use RequireGroup feed-reader
         </Else>
     </IfFile>
     <IfFile /etc/rss-bridge/is_public>