Create JSON schemas for various input files

[alexdewar]

Currently, there is no formal specification for the format of Health-GPS input files. There is a "version" field in many (though not all) of them, which suggests that there is at least an intention to provide backwards compatibility, though there are no unit tests for the config file loading code, so inadvertent changes to the format could easily be introduced.

JSON schemas provide a convenient way to check whether JSON documents adhere to a particular spec: https://json-schema.org/

If we write schemas we can use these to validate the generated input files, e.g. in tests.

Edit: I've converted this to an umbrella issue

• Add JSON schema for top-level configuration file #449
• Add JSON schemas for static risk factor models #450
• Add JSON schemas for dynamic risk factor models #451

[alexdewar]

After spending hours writing my first JSON schema manually, I realised there are tools that can help with this. I've tried this one and it seems pretty useful: https://pypi.org/project/genson/

We could auto-generate a bunch of schemas for the input files then tweak them manually, if needed.