validate_configs.py rewritten in GoLang

[andylockran]

I've not written much golang, so have tried to recreate the existing python script for validating configs using golang.

Things to discuss:

• [] Bringing in external dependencies; are there others to be using for jsonschema
• [] yaml/json reading looks to be fairly generic, but in a typed language it looks like it needs some thought.
• [] Should we get some tests, and should the validate_config compiled binary embed the openapi-schema, rather than ref it in a file, and how could we get that to work.

Anyway, first pass and don't expect this to get merged as-is.

[outofcoffee]

I suspect we might want this to be its own go module, then it can be self-contained, and not be coupled to this implementation. we should, for example, probably move the config schema(s) out to their own repo. maybe this tool lives with them to do validation, and then regardless of the engine implementation (Go, JVM), it's a standalone repo that just owns the config schema and validates files to it.