apidom-ls: AsyncAPI 2.x Reference Object optimization

[char0n]

The scope of this issue is to apply the same pattern we use for OpenAPI 3.x.y spec. All the completion, documentation and linting is concentrated in one place, instead of duplicating it in every spec object that can support referencing.

Here is a way how this is implemented in the OpenAPI 3.x.y spec - https://github.com/swagger-api/apidom/tree/0b0fbf3669fc204fbddebd0cb161af9c6291620d/packages/apidom-ls/src/config/openapi/reference

TODO:

• Optimize the usage of Reference Object
• $ref--valid rule name should be $ref--format-uri