WorkcellTask ID should be unique, and not based on the work order step ID

[aaronchongth]

As discussed here, when dealing with parallel work orders, the ID in WorkcellTask is using the step ID from the work order, which easily conflicts with other work orders.

Suggested #42 (comment), we can use a combination of the work order ID and the step ID to produce a unique workcell task ID

[Yadunund]

After some thought, I think it would be good to

• update the WorkcellTask msg to include a string work_order_id field and rename the existing id to task_id.
• Similarly also add a string work_order_id field to the WorkcellState msg which already includes a task_id field.
• Also update nexus_capabilities/Task to include both work_order_id and task_id. Should we also rename this to WorkcellTask?
• Update system orchestrator implementation to fill work_order_id in the WorkcellTask using the WorkOrder.id submitted to the system orchestrator. Also update WorkcellState.
• Update workcell orchestrator to keep track of which work_order id is being processed and update the WorkcellState publishing to reflect this.