Feature request: implement generating of top level `allOf` and `oneOf`

[Kamilcat]

Currently top level allOf and oneOf are not working, empty interfaces are generated.

[jung-kim]

I would like to second this issue.

# example yaml
    Metadata:
      required:
      - id
      - type
      type: object
      properties:
        id:
          type: string
        type:
          type: string
    PutPayload:
      allOf:
      - $ref: '#/components/schemas/Metadata'
      - type: object
        properties:
          body:
            type: string

---

# expected generated code
/** Metadata */
export interface Metadata {
  /**  */
  id: string

  /**  */
  type: string
}

/** PutPayload */
export interface PutPayload extends Metadata {
  /**  */
  body: string
} 

[Manweill]

Wellcome PRs.