implement yaml schema for settings file validation

[alexg9010]

Let's implement yaml schema for each of our settings files. Validation could be built into the pipelines. Maybe we could provide a simple website to upload the file and flag problems during verification.

Ideas and Tools:

• https://json-schema-everywhere.github.io/yaml
• https://rx.codesimply.com/
• https://blog.picnic.nl/how-to-use-yaml-schema-to-validate-your-yaml-files-c82c049c2097

[rekado]

This may be a good opportunity to revisit the yaml decision.
We did that because we hoped users would find it less confusing, but in practice we ended up with lots of problem reports that are down to syntax.

I suggest revisiting this decision and evaluating toml or plain old JSON. JSON would be the most straight-forward because yaml is a superset of JSON (if you squint). Meaning: we can use JSON already with no changes to the pipelines.

JSON has fewer moving parts, much less ambiguity, so ... as you can tell I'd jump at the opportunity to bury yaml and move on to greener pastures.