Make JSON schema more usable

[samtstern]

Follow up to #3505

TODO:

• Publish the schema somewhere
• Include $schema in firebase.json templates
• Make schema errors more visible in the logs

[samtstern]

@abeisgoat think we could publish the schema on firebase.tools?

[segevfiner]

You also need to allow "$schema" in the schema itself.

[dominicbartl]

@samtstern I created an updated PR to allow the top-level $schema property. It would be awesome if you could review this very simple change or add someone else as a reviewer. 😃

[joehan]

Happened to be working on this, but never saw this issue. - thanks for highlighting it @dominicbartl!

We've also added this to the JSON schema store, so many IDEs should pick it up by default (or once you add the necessary plugins): https://github.com/SchemaStore/schemastore/blob/master/src/api/json/catalog.json#L1615