[📑 Docs]: Adapt message validation guide for v3

[jonaslagoni]

For AsyncAPI v3, we need to adapt the message validation guide (https://www.asyncapi.com/docs/guides/message-validation) to be usable with AsyncAPI v3.

Here are the v3 structure that should be used instead:

asyncapi: 3.0.0
info:
  title: Example with Avro
  version: 0.1.0

channels:
  example:
    address: 'example'
    messages:
      avroMessage:
        payload:
          schemaFormat: 'application/vnd.apache.avro;version=1.9.0'
          schema:
            $ref: 'https://example.europe-west3.gcp.confluent.cloud/subjects/test/versions/1/schema'

Here are the main points that need to change:

• Re-add the docs/guides/message-validation.md file.
• Adapt the AsyncAPI document snippet
• Adapt the text if needed

Make sure you base your change on the next-major-spec branch and target it in your PR 🙂 If you have any questions, don't hesitate to ask.

[alaminthetrustworthy]

@alequetzalli Am new but can i join the assignee work together

[derberg]

solved with #2282
in next major branch, but considered to be fixed and closing - also for easier management of the scope for v3