Request\Add exists type field to AWS config recorders

[roneli]

Can we add an exists type field? That way we can have positive confirmation of the record in the database compared to having to handle if the record is missing for whatever reason (not in config, permissions issue, etc)

Originally posted by @bbernays in #301 (comment)

[bbernays]

Without this field this query can't tell the difference between this resource not being fetched and the resource not existing in a a specific region