[typescript-fetch] Omit readOnly properties from request models

[kota65535]

Related:

This PR omits readOnly properties from request models. Given the following OpenAPI schema and operation.

title: Task
type: object
properties:
  id:
    type: integer
    readOnly: true
  title:
    type: string

post:
  operationId: createTask
  requestBody:
    required: true
    content:
      application/json:
        schema:
          $ref: Task.yml
...

The current generated request models require the unneeded id property.

export interface CreateTaskRequest {
    task: Task;
}

This PR changes them to:

export interface CreateTaskRequest {
    task: Omit<Task, 'id'>;
}

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