Add JSON schema for output files

[marcusrbrown]

As a developer, I would like to validate the output of the publishing tool. As a toolsmith, I would like to improve DX by leveraging JSON schema to enhance tools and editors.

• Add a schema for index.json and other JSON output. If the output is only used during build, the schema is probably overkill.
• Add schema validation to the build step
• Modify deployment steps to publish schemas to a well-known address (e.g. ts-defold.dev/library/schema/)