Correct Indentation in `Agent` schema

[Purna]

in the core.yaml file, the schema for Agent is defined as follows.

 Agent:
      description: Describes an order executor
      allOf:
        - $ref: '#/components/schemas/Person'
        - $ref: '#/components/schemas/Contact'
        - type: object
          properties:
            rateable:
              $ref: '#/components/schemas/Rateable'

The type key should be on the same indentation level of allOf.