Provide JSON validation for config files

[MahdiBM]

Is your feature request related to a problem? Please describe.
This extension should provide JSON schemas for validation, for JSON config files related to this extension.
For example for .sourcekit-lsp/config.json, when sourcekit-lsp supports that.
Then users will have an easier time writing config files.

Please Note that VS Code does not fully support newer version of JSON schema specification and we'll probably need to stick to version draft-07.

For the JSON validations to be enabled, this extension can use the package.json file. See rust-analyzer as an example.

Describe alternatives you've considered
Users can manually use "$schema": "link/to/schema" in the config JSON files to manually enable schema validations. See the link for a full of the options.

Additional context
Add any other context or screenshots about the feature request here.