Redact delayed_jobs handler column in query logs

[kathap]

The serialized handler column is verbose and clutters the statement log. Strip its value from logged delayed_jobs INSERT/UPDATE statements via a Sequel extension, enabled through DB.connect when query logging is on.

• A short explanation of the proposed change:
  The serialized handler column is verbose and clutters the statement log. This change does two things:

  1. Strip the handler value from logged delayed_jobs INSERT/UPDATE statements via a Sequel logging extension, enabled through DB.connect when query logging is on.
  2. Add a concise structured log line per enqueued job. Because the handler value is no longer in the statement log, we actively collect the useful fields of each background job and write them to a dedicated enqueued background job log line.

• An explanation of the use cases your change solves
  The handler column holds the full serialized job payload, which produces very long, noisy log lines that make the statement log hard to read and inflate log volume. Stripping the handler value from logged delayed_jobs statements cleans that up.
  However, the handler value also carried fields that are useful when debugging worker/job behaviour (job class, operation, resource guid, retry number, user, request id, etc.). To keep that information available without the verbose payload, a new hash_for_logs method collects only those fields from each job and the Enqueuer writes them as a single structured log line. Net result: the statement log is clean, and every created job remains traceable.

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