Retry `atLeastOnce` background tasks on timeout and exceptions.

[losfair]

Currently, an atLeastOnce background task will be retried if the Blueboat host process exits during execution, but will NOT be retried in the following circumstances:

• An exception is thrown.
• The worker process crashed.
• The 30-second limit is reached.

Supporting retry in these cases requires re-enqueueing the task to Kafka.