Work order ID and task ID

[aaronchongth]

Addresses #63 (comment)

This will help with creating unique workcell task IDs, to be used for signals in parallel work orders, #63

• Added work order ID, renamed ID to task ID where applicable, migrate changes and populate fields
• removed step ID per discussion, update tests
• generate task ID as {work_order_id}/{process_id}
• remove id from WorkOrder msg, since that duplicates the purpose of number in the model
• change number to id in WorkOrder model, use that for work_order_id instead, updated tests and readme

Verify

# Run demo
ros2 launch nexus_integration_tests launch.py headless:=0

# Run work order
cd ~/ws_nexus/src/nexus/nexus_integration_tests/
ros2 action send_goal /system_orchestrator/execute_order nexus_orchestrator_msgs/action/ExecuteWorkOrder "{order: {work_order: '$(cat config/pick_and_place.json)'}}"

# Check topics, verify that work order ID is populated with 23, task ID is populated with test-1/{processId}
ros2 topic echo /workcell_1/workcell_state
ros2 topic echo /workcell_2/workcell_state