Fixes

Fast follow from #643 to implement a suggestion by @sarayourfriend

⚠️ Because this introduces a breaking change to the configuration variable, we must make sure the variable is not configured in production before merging. If it is configured, we need to make sure no affected DAGs (check_silenced_dags, any silenced DAGs) are running while we deploy these changes and update the variable interface. Discussion. ⚠️

Description

#643 introduced an Airflow variable (silenced_slack_alerts) that allows configuring a DAG to skip Slack reporting of errors. The implementation in that PR only allows for skipping Slack reporting for all error messages, but in reality we're unlikely to want this behavior. It's much safer to be able to silence specific known errors.

This PR changes the shape of the silenced_slack_alerts:

For each dag_id you must now provide both an issue and a list of errors. A slack alert will not be sent if it matches any of the predicates in the errors list for the given DAG.

Because our on_failure_callback includes information like the ExceptionType and task id in the message, we can use this to selectively silence messages matching those parameters as well.

Testing Instructions

• Create an Airflow variable named silenced_slack_alerts in the Admin > Variables UI. For my tests I used this configuration:

{
  "audio_data_refresh": {
      "issue": "https://github.com/WordPress/openverse-catalog/issues/438",
      "errors": ["A test exception"]
  }
}

• For the DAGs you've configured above, force an error to be thrown by editing the code to manually raise one. Make sure that it includes the configured predicate.
• Run the DAG and verify that you can see a message in the logs saying Skipping Slack alert for <dag_id>.
• Play around with your test error and the errors configuration to test that errors that do not match any of the predicates are still reported to Slack.

Now test check_silenced_dags DAG:

• Edit your configuration to link to a GH issue that is closed. Run the DAG and verify you get a Slack alert indicating that the alerts can be turned back on.
• Edit your configuration to link to a GH issue that is open. Run the DAG and verify you do not see a Slack alert.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

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