fix: jitsi-meet-tokens - the first installation check (#7618)

debian/jitsi-meet-tokens.postinst

         db_stop
 
         if [ -f "$PROSODY_HOST_CONFIG" ] ; then
-            # search for --plugin_paths, if this is not enabled this is the
+            # search for the token auth, if this is not enabled this is the
             # first time we install tokens package and needs a config change
-            if grep -q "\-\-plugin_paths" "$PROSODY_HOST_CONFIG"; then
+            if ! egrep -q '^\s*authentication\s*=\s*"token"' "$PROSODY_HOST_CONFIG"; then
                 # enable tokens in prosody host config
                 sed -i 's/--plugin_paths/plugin_paths/g' $PROSODY_HOST_CONFIG
                 sed -i 's/authentication = "anonymous"/authentication = "token"/g' $PROSODY_HOST_CONFIG