Jsonschema-to-openapi

Added
- Create empty items, as it must always be present for type: array
- Rewrite exclusiveMinimum/exclusiveMaximum
- Rewrite if/then/else as oneOf + allOf
- Rewrite const as single element enum

Fixed
- Implemented [cloudflare/json-schema-walker] to make sure all subschemas are
processed

[cloudflare/json-schema-walker]: https://github.com/cloudflare/json-schema-toolscloudflarejson-schema-walker

Added
- Convert `dependencies` to an allOf + oneOf OpenAPI-valid equivalent