Add configuration option to disable threshold

[naibaf0]

Can we introduce a way (probably env var at this point) to disable the CLAIR_THRESHOLD?

In my case I mainly use klar for fetching of all vulnerabilities that are found for an image and whitelisting/processing happens at a later stage. It would be nice, if we could disable the threshold instead of setting a very high threshold and adding error handling to my shell script to work around it, which is what we are currently doing.