Adding dedup on images already assessed

[afieffe]

Skipping images with an evaluation already available in the time windows specified.

[jvogt]

Logic LGTM, but two suggestions:

1. Let's make this optional (CLI flag), and turned off by default. Reasoning is container vulns endpoint is extremely verbose and even small lacework accounts can sometimes hit 100 pages (maximum pagination) of data returned for a 24 hour query. This takes a long time to paginate through (5-10 minutes) and may be an incomplete dataset. Don't want to negatively affect existing users.

2. Can you add some documentation to the readme regarding the above mode and how it works? Also some word on how it compares to using the local cache.