Add new decorator to parse message data using a supplied Pydantic model

Description

Extend the added pubsub_messages function to add a new decorator which extracts the data in the MessagePublishedData.message.data field from the event, and deserialises it into a supplied Pydantic model, passing that deserialised Pydantic model instance to the handler.

Further details

This should be an overload of the original decorator, discriminated by an argument which is type, bound to a Pydantic model type.

Task list

Acceptance criteria

• Decorator overload to perform message payload validation/parsing via a Pydantic model exists
• Validation errors should be caught and logged as exceptions, with a 400 response to the caller

Links/references