Loop detection

[mhamann]

Add logic to detect when an API might be calling itself (directly or via another API) in a loop, and terminate the loop.

This can be done through injection of unique headers for every hop through the gateway.

For example:

Client request -> GW: GET /api1 GW inject header: X-ApiGw-Loop: get_api1 GW request -> GW: GET /api2 GW inject header: X-ApiGw-Loop: get_api1 get_api2 GW request -> GW: GET /api1 GW analyzes X-ApiGw-Loop and sees get_api1 is already present GW response: 508 Loop detected (or similar)