feat(rulesets): validate unresolved AsyncAPI document

[magicmatatjahu]

Fixes #2261.

Checklist

• Tests added / updated
• Docs added / updated

Does this PR introduce a breaking change?

• Yes
• No

Screenshots

The following AsyncAPI document is invalid and Spectral should throw errors due to invalid defined references (in impossible places):

asyncapi: '2.0.0'
channels: 
  someChannel:
    publish:
      $ref: '#/components/x-operations/someOperation'
components:
  'x-operations':
    someOperation: ...

and Spectral will return errors:

[
  {
    message: 'Referencing here is not allowed',
    path: ['channels', 'someChannel', 'publish', '$ref'],
    severity: DiagnosticSeverity.Error,
  }
]

[jonaslagoni]

@magicmatatjahu is this ready to be reviewed or do you still need to do some work regarding #2262 (comment)?

[magicmatatjahu]

@jonaslagoni Yeah, when I will find time, I will create PR with uniqueId for schema function.

[jonaslagoni]

Any update on this one @magicmatatjahu? Or do you want to close it?

[mnaumanali94]

Closing as stale. Feel free to open if needed. @jonaslagoni