Update auditors to support types

[markofu]

W should update the auditors to have the concept of supported account types, all collectors.

Something along the lines of

class IAMAuditor(BaseAuditor):
    auditor_type = AuditorTypes.AWS_Account

with auditor_type being one of AWS_Account, AWS_Region, Global as the currently supported auditors.

For example, the VPC Flow Log auditor should be a AWS_Region auditor, and the IAM should be AWS_Account auditor, with the Domain Hijacking being a Global.