Validate use of NotResource and NotAction based on AWS best practices

[raghavkaul]

This auditor validates two AWS policy elements, and gives the user feedback to align with AWS documentation best practices. NotResource and NotAction are difficult to write policies for correctly because they implicitly Allow access to everything that is not specified in the Statement, and then revoke access.

I chose to make these 1 PR because they are both considered "advanced" policy elements by AWS and using either with 'Effect': 'Allow'are both explicitly discouraged in the documentation. However, NotResource is targeted towards identity-based policies, whereas NotAction is targeted towards resource-based policies and trust relationships. So, I would be open to splitting this up somehow, e.g. by putting the checks into different community auditors Py files. Or, if we aren't ready for parliament to check resource-based policies, then we can skip NotAction entirely.

[0xdabbad00]

Thank you @raghavkaul ! LGTM, this can be merged @steiza