Tuple validation changes in JSON Schema specification

[cyberixae]

The way tuples are defined have been going through some changes https://json-schema.org/understanding-json-schema/reference/array.html#tuple-validation

Previously the tuple [string, number] would be defined as

{
  "type": "array",
  "items": [
    { "type": "string"},
    { "type": "number"}
  ]
}

With some of the newer drafts the same tuple [string, number] would be defined as

{
  "type": "array",
  "prefixItems": [
    { "type": "string"},
    { "type": "number"}
  ]
}

The io-ts-from-json-schema converter currently only supports the old tuple schema definition.

There are also some other changes related to how other keywords are interpreted in relation to the tuple definition.