Create Secondary Child Association (multi-file)

POST /nodes/{sourceNodeId}/secondary-children
=>
{
  "childId":"f2d626fb-d766-4231-af07-7ac3aab41766",
  "assocType":"my:assocType"
}

Response example:
<=
{
  "childId":"f2d626fb-d766-4231-af07-7ac3aab41766",
  "assocType":"my:assocType"
}

basePath: /alfresco/api/-default-/public/alfresco/versions/1
tags:
  - name: child associations
    description: Node child associations
paths:
  '/nodes/{parentId}/secondary-children/':
    post:
      tags:
        - child associations
        - 5.2 changes
      summary: Add secondary child association
      description: |
        Add secondary child association between parent and child node for given association type.
      operationId: addChildAssoc
      produces:
        - application/json
      parameters:
        - name: childId
          in: path
          description: The identifier of a node.
          required: true
          type: string
        - in: body
          name: assocChildBody
          description: The child node id and assoc type.
          required: true
          schema:
            required:
              - childId
              - assocType
            properties:
              childId:
                type: string
              assocType:
                type: string
      responses:
        '201':
          description: Successful response
        '400':
          description: Invalid parameter, eg. unknown assocType
        '404':
          description: If **parentId** or **childId** does not exist
        '409':
          description: Association already exists (same assoc type between same two nodes ids)
        '422':
          description: Model integrity exception
        default:
          description: Error response
          schema:
            $ref: '#/definitions/Error'