Stricter validation of JSON Schema

[jsoriano]

We have found some cases where invalid JSON Schema syntax is not detected. This could lead to unexpected specifications, for example:

• [Bug] Suspected invalid 'required' JSONSchema attribute #957
• fix(data_stream manifest): move required_var minItems #965

Perform stricter validation of JSON Schema, so we can earlier detect this kind of issues.

[jsoriano]

A way to enable JSON Schema validation might be with these changes: #972

[jsoriano]

We could use some linter like https://github.com/sourcemeta/jsonschema/blob/main/docs/lint.markdown in CI, we would need to render all the JSON files for all the versions. Thanks @andrewkroh for suggesting the tool!