What does this PR do?

• Stores last verification error message in attribute
• Improves message of DNS validator when it fails
• Moves all DNS verification to single re-usable method
• Support new action in certificate worker (verification) alongside current action (cert generation)
• Adds ability to override verification domains in certificate worker for easy cross-region support
• Instantly upsert certificate from worker, to quickly show changes to logs in UI
• comma-separated list support for dns client, for multi-level verification
• Re-orders validation to look for CAA issues first
• Rule's $updatedAt to have certificate's updatedAt if its later
• Add constants for rule status, and document each status

Test Plan

• new proxy tests implemented for e2e validation flows (with coredns)

Related PRs and Issues

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Checklist

• Have you read the Contributing Guidelines on issues?
• If the PR includes a change to an API's metadata (desc, label, params, etc.), does it also include updated API specs and example docs?