Add a rule to validate message's examples

[magicmatatjahu]

User story.
As a user I want to know if the examples defined in the message object are valid.

Is your feature request related to a problem?
The following AsyncAPI document is invalid and Spectral should throw errors:

asyncapi: "2.0.0"
info:
  title: Bad API
  version: "1.0.0"
components:
  messages:
    someMessage:
      payload:
        type: string
      headers:
        type: object
      examples:
        - payload: 2137 # should be string
          headers: someHeader # should have object shape

Additional context
Part of #2100

[stoplight-bot]

🎉 This issue has been resolved in version @stoplight/spectral-rulesets-v1.10.0 🎉

The release is available on npm package (@latest dist-tag)

Your semantic-release bot 📦🚀