Use `finding_data` to generate response

This commit introduces a new finder class to be used while we are
transitioning from using artifacts to utilizing data stored in the DB.

This new finder class will mainly use the data stored in the database
except the remediations are still read from report artifacts by using
the `multi_read` method.

With this change, we will also no longer show the findings of purged
security scans.

Changelog: fixed
EE: true