erp5.TODO: Add release-critical entry about frontend.

The way to request frontend has changed a lot since this code was written.
Find a way to not depend on how frontend work, to not have to keep SRs
synchronised with frontend flavours.

stack/erp5/TODO

 Release critical:
 - default number of test relation databases must be 0
   This requires erp5 test nodes to be updated to a version where the correct number of databases is requested
+- update or drop frontend integration
 
 General:
 - varnish/squid