Add `yamlfmt` configuration schema

[becknik]

Description of the JSON schema.

The schema for the formatting part of the configuration options is available here: https://github.com/google/yamlfmt/blob/main/schema.json
This doesn't seem to be the correct schema for all the configurations options available, but only of the options accepted under the format: root key...

Supporting information.

Descriptions of the schema can be found here: https://github.com/google/yamlfmt/blob/main/docs/config-file.md#configuration

Are you making a PR for this?

No, someone else must create the PR.

[Vessel9817]

This was completed in #5639. However, you're right that Google's own yamlfmt schema is missing some properties. Namely, the top-level match_type property (which we implemented), as well as all properties associated with the basic formatter.