Debug-headers in ORM

[nsg]

When a rule owner does not get the expected result from ORM, it is currently difficult to identify why this is happening. A debug feature that sets one or more headers, identifying the namespace/rule that the request matched, would be very helpful in these cases.
The debug feature should not be publicly available and preferably activated by including an appropriate header in the request. For example, if we set "X-ORM-DEBUG: True" the response should include the debug headers identifying the matching rule.

(imported from internal bug-tracker)