Create and publish .regal/config.yaml schema to JSON schema store

[anderseknert]

We should create a JSON schema for the Regal configuration file format and have it published to the JSON schema store. This allows tools like the YAML language server (which is used by editors like VS Code and Zed) to automatically provide auto-completions and corrections based on the schema when the filename matches .regal/config.yaml.

Note that we should avoid having the schema auto-generated from Go structs, as both categories and rule names are dynamic. I'd suggest we use properties for all known categories and rule names, likely generated from the default config. We could provide one strict version, where only these names are allowed (to help identify typos), and one version where additional properties are allowed, for those who might have custom rules.