Pick up schema from $schema prop like with JSON

In case of JSON files it's possible to discover the support for $schema naturally by following the Trigger Suggest command:

https://user-images.githubusercontent.com/1932383/126984982-a9660d62-b473-469c-833d-9665adcf9ff2.mov

Tho with YAML, even if you were to write out the comment you would see no autocompletion. To achieve same you should write out # yaml-language-server: $schema=https://json.schemastore.org/tsconfig. Which should be memoized, or stored as a snippet. or you should mess with configuration of this extension, which should be discovered in the first place and is not as portable as $schema is with json.

https://user-images.githubusercontent.com/1932383/126985088-6160c7ba-70bf-4ad9-9410-134386a13ff9.mov

Describe the solution you would like

It would be great to support similar UX to what exists with JSON. where suggestions help you discover $schema support and then by specifying $schema, schema is used to validate the file. no need to mess with extentsion configuration or comments.

Start by tracing the existing JSON "Trigger Suggest" behavior and the YAML language-server handling of $schema and yaml-language-server comments. Define how a YAML $schema property should trigger schema discovery and validation, then verify the behavior with the extension's existing test coverage; the issue names no specific files or tests.