[Schema Inaccuracy] Fields not marked as required

[cipriancaba]

Schema Inaccuracy

The response fields are not marked as required thus creating | undefined types in code generation tools

Expected

For example, the tag definition:

 tag:
      title: Tag
      type: object
      x-tags:
      - Tags
      description: A tag allows you to label your contacts, companies, and conversations
        and list them using that tag.
      properties:
        type:
          type: string
          description: value is "tag"
          example: tag
        id:
          type: string
          description: The id of the tag
          example: '123456'
        name:
          type: string
          description: The name of the tag
          example: Test tag
        applied_at:
          type: integer
          format: date-time
          description: The time when the tag was applied to the object
          example: 1663597223
        applied_by:
          "$ref": "#/components/schemas/reference"

should be:

tag:
      title: Tag
      type: object
      x-tags:
      - Tags
      description: A tag allows you to label your contacts, companies, and conversations
        and list them using that tag.
      properties:
        type:
          type: string
          required: true
          description: value is "tag"
          example: tag
        id:
          type: string
          required: true
          description: The id of the tag
          example: '123456'
        name:
          type: string
          required: true
          description: The name of the tag
          example: Test tag
        applied_at:
          required: true
          type: integer
          format: date-time
          description: The time when the tag was applied to the object
          example: 1663597223
        applied_by:
          required: true
          "$ref": "#/components/schemas/reference"

Reproduction Steps

Please see attached conversation
openapi-ts/openapi-typescript#1422 (comment)

And repro repo
https://github.com/cipriancaba/openapi-typescript