[feature] Json schema support

[Freed-Wu]

Describe your proposed improvement and the problem it solves.

pandoc has a usage as following:

defaults.yaml:

---
to: beamer
pdf-engine: xelatex

pandoc -ddefaults.yaml -oXXX.pdf XXX.md

Can defaults.yaml have a json schema and been published in schemastore? Like alacritty?

This is a reference about latexindent.yaml cmhughes/latexindent.pl#206

The steps are following:

• Create a json schema
• Add its URL to schemastore.