Add Tuple serialization

[elbywan]

Purpose

Adds the self.to_openapi_schema for the Tuple type.

@dukeraphaelng This should solve #9, let me know if this looks good to you I'll merge afterwards.

Note

OpenAPI v3.0.x does not support the proper way to express tuples as a json schema.

Passing an array of items is forbidden by the specification:

• Value MUST be an object and not an array. Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema. items MUST be present if the type is array.).
• Related issue: Make schema object compatible with JSON Schema specification OAI/OpenAPI-Specification#1026.
• Support has been recently added with the release of OpenAPI 3.1., but this is beyond the scope of this PR.

As a workaround this PR serializes tuples into an array with fixed bounds and items that can be one of the tuple types.

Example

puts Tuple(Int32, String, Tuple(Bool | Array(Float64))).to_openapi_schema.to_pretty_json

{
  "maxItems": 3,
  "minItems": 3,
  "type": "array",
  "items": {
    "oneOf": [
      {
        "type": "integer"
      },
      {
        "type": "string"
      },
      {
        "maxItems": 1,
        "minItems": 1,
        "type": "array",
        "items": {
          "oneOf": [
            {
              "type": "array",
              "items": {
                "type": "number"
              }
            },
            {
              "type": "boolean"
            }
          ]
        }
      }
    ]
  }
}

[dukenguyenxyz]

this is awesome! thank you so much