Disable POST /notify endpoint by configuration

[fgalan]

STH API exposes a POST /notify endpoint which process directly notification (instead that the using mechanisms of feeding STH database through Cygnus).

This is good for small setups in STH not oriented to production. However, in production is not conveniente as the aggregation steps needed for notifications could severily impact in the STH performance.

Thus we need to be able to disable POST /notify by configuration.

[mrutid]

I think that STH "as it is" could be used in production if you make a clear distinction between processing and query nodes, so nodes used for data ingestion and aggregation don't serve query requests. Maybe is a good idea to configure not only "query only" (disabling /notify), but "aggregation only" or "both"