feat(19240): Add validity checks to the policies in the designer

[vanch3d]

See https://hivemq.kanbanize.com/ctrl_board/57/cards/19240/details/

This PR is an enabler for the full integration of the policy designer with the API. It provides a UX for running validity checks on an existing policy (both Data Policy and Behaviour Policy), verifying that every "node" in the designer is properly configured and building a valid payload ready for requests.

https://www.loom.com/share/4014b86e1cfe4c90a8bec6a884a10201?sid=488cc87e-dc16-475b-b427-9a1e474ad94b

Design

• The validity check process is based on walking the graph from a target policy until all connected nodes are discovered
• Starting from the policy, each connected node is checked for its correctness, both internal configuration (e.g. the model for a Behavior Policy node) and connectivity with other dependencies (e.g. a Client Filter for a Behavior Policy node).
• On the canvas, nodes being processed are marked on the fly with appropriate visual feedback showing in progress, valid or error
• Error messages are generated for every misconfiguration
• if there is no error, a JSON payload matching the node to the relevant part of the API request is generated
• For the relevant nodes (e.g. a transform operation), the required "resources" (e.g. the Schema nodes for serialiser/deserialiser and the JS Script for the functions) are also verified and they payload generated
• When the process is complete (all connected nodes have been checked), a report is produced
• If fully valid, all the collected payloads are combined and now ready to be used with the appropriate API endpoint(s)
• if errors are present in the report, a list is provided to the users, with a description and links to both the node on the graph and its configuration panel

Out-of-scope

• the current UX for the check report, using a toast, is not satisfactory from a usability and acceptability point-of-view. A better alternative has been proposed and will be implemented in a further ticket, see https://hivemq.kanbanize.com/ctrl_board/57/cards/19334/details/
• handling the API request(s) and their errors will be dealt with in a separate ticket, see https://hivemq.kanbanize.com/ctrl_board/57/cards/19497/details/
• Generating canvas from a loaded policy will be dealt with in a separate ticket, see https://hivemq.kanbanize.com/ctrl_board/57/cards/19500/details/

After

[h2xd]

Going on a second journey later on