Scan for secrets

With these two new rake tasks I am trying to find apps that are indadvertedly logging secrets. Of course they shouldn't do this and, of course, the airbrake gem is filtering quite some stuff already but we saw it happening nonetheless and that's why I wanted to take a closer look.

I am sure that the algorithm can be improved a lot. The app-finding query could perhaps start over again at some point in time to skip all apps that are already found to be vulnerable. This would greatly reduce (de-)serialization of the Notice model. But we can do this later.

If you have better names for the namespace or the tasks; please do tell! I am not really happy with them now.