Add air.toml's json schema to schemastore for autocompletion and diagnostics

[DavisVaughan]

This is a bit of a future looking goal once things stabilize.

We should create a "json schema" for our toml file and get it on https://www.schemastore.org/json/ by sending a PR to https://github.com/SchemaStore/schemastore. We can do this by tagging our TomlOptions fields using the schemars crate which integrates with serde-json, and then emitting a json schema for that struct to a file.

The reason we'd want to do this is to get autocompletion and diagnostics in our air.toml file. With the Even Better TOML extension in VS Code and in some IDEs natively like PyCharm, if you have a json schema for your file on schemastore, then it will automatically start providing autocompletions and diagnostics for that file. Super useful so you don't have to guess if your toml config is right or not.

pypa/hatch#731 (comment)

[lionel-]

ooh that's nice!

[DavisVaughan]

IIUC in our vs code extension we can even register our schemastore as the toml validator and even better toml will pick it up. ruff doesn't do this from what I can tell so we'd be experimenting a bit but it would be nice if that made it mostly automatic https://taplo.tamasfe.dev/configuration/developing-schemas.html#visual-studio-code-extensions