Log nginx diff at info level.
Log nginx diff at info level.

There have recently been many problems around getting 502's and 504's partly
caused by nginx reloading. Nginx has also been noticed to reload far more
frequently than expected (10-20 times an hour) and it is very difficult to
investigate the cause of the reload without this log.

Closes https://github.com/sky-uk/umc-core/issues/2672

sky-uk/feed,sky-uk/feed