feat(snyk/trivy pipeline): check for images in `/kratix/output` instead of input

both the snyk and the trivy pipeline image are looking for image keys in the documents they find in the /kratix/input directory.

this a reminiscent from the days the kratix pipelines would copy whatever was available in the previous container output into the next container input; now that this is no longer how kratix works, this behaviour no longer makes much sense;