Support $schema reference to JSON schema

Currently JSON schema for a YAML file must be specified externally, either via settings or from the public schema store.

I’d like to be able to specify the schema to use in the YAML document itself. This is possible with JSON documents by specifying a $schema property, e.g.

{
  "$schema": "http://some.org/schema",
  "prop1": "value1"
  ...
}

It seems reasonable to me that the same convention could be supported for YAML documents (as this is defined as part of the JSON schema spec itself):

$schema: http://some.org/schema
prop1: value1
...

[apupier]

implemented using # yaml-language-server: $schema=http://some.org/schema format

[ssbarnea]

Lets open a sister ticket on YAML meta repository itself, maybe YAML spec authors can help us make a good/future proof decision?