Make cron spec available for scheduled workflows

[apoliakov]

Requested by a user in the off-topic discord channel:

Hi - not sure where else to put it. When I specify a scheduled workflow, the function is added to the DBOS system database as job_queue, The cron specification, however, is not available in the system database as property of a workflow (or job). For debugging reasons, esp. in case of time travel, that might come in handy as the specification might be important to interpret the workflow_status.