rule evaluation status does not support artifacts + webhook event doesn't store artifact version

[jhrozek]

Describe the bug Once we land PR stacklok/mediator#692, we'll have a pretty good support for artifacts. What will still be missing is the ability to tie the rule evaluation status to artifacts so that we can query the status of policies pertaining the artifacts correctly.

We'll need to:

• [x] extend the rule_evaluation status with the other _id columns. It's debatable whether to do that or a single ID, but we'll start with the multiple _id columns so that we can take advantage of cascaded deletes
• [x] provide sqlc-generated CRUD methods.
• [x] use those in the handlers so that clients can query the artifacts
• [x] store the artifact versions in the webhook handler so that artifacts published after the initial reconciliation can be processed

[jhrozek]

issue stacklok/mediator#761 is now part of epic issue stacklok/epics#29