Add schema for the CloudCannon configuration file

[rphillips-cc]

Add externally hosted schema for the CloudCannon configuration file.

• Issue: https://github.com/SchemaStore/schemastore/issues/4225
• Externally hosted schema: https://github.com/cloudcannon/configuration-types/releases/latest/download/cloudcannon-config.schema.json

[github-actions[bot]]

Thanks for the PR!

This section of the codebase is owned by @madskristensen and @hyperupcall - if they write a comment saying "LGTM" then it will be merged.

[hyperupcall]

Thanks