Add support for AsyncAPI 2.4

[char0n]

AsyncAPI 2.4 is out. The goal of this issue is to provide support for in ApiDOM.

• namespace
• rest of packages
• apidom-reference
• apidom-ls
• SwaggerIDE followup

Resources:

• https://github.com/asyncapi/spec/releases/tag/v2.4.0
• https://www.asyncapi.com/blog/release-notes-2.4.0
• asyncapi/spec@v2.3.0...v2.4.0