Add support for JSON:API media type

[gletournel]

The generated API client does not comply with JSON:API specification.

When generating an API client for an OpenApi specification complying with JSON:API, the client ignores the JSON:API media type (application/vnd.api+json) declared in the request body definition and replaces it with the default application/json type.

This causes errors with API servers that strictly comply with the JSON:API specification. These fail to process requests with an unexpected content type, and in this specific case, they return a "415 Unsupported Media Type" error.

Let’s take the following spec example.

paths:
  /pets:
    post:
      summary: Add a new pet
      operationId: addPet
      requestBody:
        required: true
        content:
          application/vnd.api+json:
            schema:
              type: object
              properties:
                data:
                  $ref: '#/components/schemas/Pet'
      responses:
        '200':
          $ref: '#/components/responses/PetResponse'
        default:
          $ref: '#/components/responses/ErrorResponse'

The generated client looks like this.

export class Api<
  SecurityDataType extends unknown,
> extends HttpClient<SecurityDataType> {
  pets = {
    addPet: (
      data: {
        data: Pet;
      },
      params: RequestParams = {},
    ) =>
      this.request<
        {
          data: Pet;
        },
        {
          errors: Error[];
        }
      >({
        path: \`/pets\`,
        method: "POST",
        body: data,
        type: ContentType.JsonApi,
        ...params,
      }),
  };
}

In the request properties, we get type: ContentType.Json while we expect the client to send the application/vnd.api+json media type.