[FEATURE] Kafka: add schema `compatibility` field to message binding

[ivangsa]

Why do we need this improvement?

When using a schema registry, the compatibility mode is part of the contract
between producers and consumers. There is currently no way to document it in
an AsyncAPI message binding.

How will this change help?

Teams reading the AsyncAPI document know immediately what compatibility
guarantee the schema is registered under. Tooling that registers schemas
from AsyncAPI documents can apply the correct compatibility setting without
external configuration.

Screenshots

No response

How could it be implemented/designed?

Add a compatibility field to the Message Binding Object.

Field Name	Type	Description	Applicability [default]	Constraints
compatibility	string	The schema compatibility mode used when registering this schema.	OPTIONAL	MUST be one of BACKWARD, BACKWARD_TRANSITIVE, FORWARD, FORWARD_TRANSITIVE, FULL, FULL_TRANSITIVE, NONE

messages:
  PaymentEvent:
    bindings:
      kafka:
        schemaIdLocation: 'payload'
        schemaLookupStrategy: 'TopicNameStrategy'
        compatibility: 'BACKWARD'
        bindingVersion: '0.6.0'

The enum values follow the compatibility types defined by Confluent Schema
Registry and supported by Apicurio Registry and Karapace.

🚧 Breaking changes

No

👀 Have you checked for similar open issues?

• I checked and didn't find a similar issue

🏢 Have you read the Contributing Guidelines?

• I have read the Contributing Guidelines

Are you willing to work on this issue?

Yes I am willing to submit a PR!

[dalelane]

This looks good to me. (I'll review the PRs once I've read through the other issues first as they're combined, but this one looked like an uncontroversial easy start!)