feat: Add state property to Order schema

[rashap224]

Issue Reference : Resolves #310

• This PR adds a state property to the Order schema in the draft specification. The state property references the State schema and is intended to represent the current state of an order, such as 'Pending', 'Processing', or 'Shipped'.
• This addition enhances the draft specification by providing a more granular way to track the lifecycle of an order.

Changes Made

• Updated Order.yaml to include the state property.
• The state property references the State schema (/schema/State.yaml).

Adding Order.state aligns the draft spec with the stable spec and provides better clarity on order lifecycle management.

[rashap224]

@ravi-prakash-v Kindly review the PR when possible. This adds Order.state to the draft spec, as discussed. Let me know if any changes are needed.