feat(20275): Improve the UX flow for draft and edited policy

[vanch3d]

See https://hivemq.kanbanize.com/ctrl_board/57/cards/20275/details/

The PR clarifies the status of the Data Hub Designer when dealing with draft or loaded/modified policies.

• A status is added to the Data Hub store, indicating whether the canvas contains aDRAFT, aLOADEDpolicy or aMODIFIED` policy.
• An info panel is added to the toolbar, indicating the status of the Designer's canvas and, if appropriate, the name and type of a loaded policy
• The primary CTA on the policy table changes state depending on the status (Create a new policy, Continue on draft, Clear the draft)

The PR also improves several aspects of the UX

• The texts in the toolbar cannot be selected by the user; it improves usability
• The Designer building buttons are disabled until a data policy or behavior policy is created on the canvas
• A default template is added to any newly created JS Function node

Out-of-scope

• clearing the canvas doesn't have any confirmation guard. It will be added in a subsequent ticket
• the name of a policy, as displayed in the toolbar, can stretch a long way. Overflow/ellipsis will be added in a subsequent ticket

Before

After