[CLEANUP] config: catch and report some possibly wrong rule ordering

[CLEANUP] config: catch and report some possibly wrong rule ordering

There are some configurations in which redirect rules are declared
after use_backend rules. We can also find "block" rules after any
of these ones. The processing sequence is :
  - block
  - redirect
  - use_backend

So as of now we try to detect wrong ordering to warn the user about
a possibly undesired behaviour.