Ensure it is possible to write server-side code that can validate a sequence of A2UI messages based on a generic schema

[jacobsimionato]

We should ensure that on the server side, we can write a generic validation function that accepts a sequence of A2UI messages and a schema, and validates that they conform to the schema.

e.g in pseudocode:

validate(List<A2uiMessage>, JsonObject catalog)

It should check:

• JSON schema conformance
• Valid references between components by ID
• Valid references to the data model
• Valid references to functions

[jacobsimionato]

CC @nan-yu

[jacobsimionato]

Resolved by #510