[POR-2128] ECR Scan status endpoint

[jose-fully-ported]

What does this PR do?

This builds upon #3979 and also requires https://github.com/porter-dev/cluster-control-plane/pull/491 before merging.

For usage, we'll want to grab all the registries and check their status. That is a naive approach for now, as in theory an attached registry doesn't need to be an AWS one. The registries table doesn't note whether a registry is related to AWS or not either.

A follow-up PR should be done to simplify that so we can check just AWS registries and get some sort of combined status.