Support listing of secondary children

  '/nodes/{parentId}/secondary-children':
    get:
      tags:
        - child associations
        - 5.2 changes
      summary: List secondary children
      description: |
        Returns a list of secondary child nodes that are associated with the current parent node, via a secondary child association.
      operationId: listSecondaryChildAssociations
      produces:
        - application/json
      parameters:
        - name: parentId
          in: path
          description: The identifier of a node.
          required: true
          type: string
        - name: assocType
          in: query
          description: Restrict the returned results to only those of the given association type
          type: string
          required: false 
        - name: where
          in: query
          description: |
            Optionally filter the list by assocType. Here's an example:

            *   where=(assocType='my:assoctype')
          required: false
          type: string          
        - $ref: '#/parameters/nodeAssocMinimalEntryIncludeParam'
        - $ref: '#/parameters/fieldsParam'
      responses:
        '200':
          description: Successful response
          schema:
            $ref: '#/definitions/NodeChildAssocPaging'
        '400':
          description: Invalid parameter, eg. unknown assocType
        '404':
          description: If **parentId** does not exist
        default:
          description: Error response
          schema:
            $ref: '#/definitions/Error'
definitions:
NodeChildAssocPaging:
    type: object
    properties:
      list:
        type: object
        properties:
          pagination:
            $ref: '#/definitions/Pagination'
          entries:
            type: array
            items:
              $ref: '#/definitions/NodeChildAssocMinimalEntry'
  NodeChildAssocMinimalEntry:
    type: object
    required:
      - entry
    properties:
      entry:
        $ref: '#/definitions/NodeChildAssocMinimal'
  NodeChildAssocMinimal:
    type: object
    properties:
      id:
        type: string
      parentId:
        type: string
      name:
        type: string
      nodeType:
        type: string
      isFolder:
        type: boolean
      isFile:
        type: boolean
      modifiedAt:
        type: string
        format: date-time
      modifiedByUser:
        $ref: '#/definitions/UserInfo'
      createdAt:
        type: string
        format: date-time
      createdByUser:
        $ref: '#/definitions/UserInfo'
      content:
        $ref: '#/definitions/ContentInfo'
      association:
        $ref: '#/definitions/ChildAssocInfo'
  ChildAssocInfo:
    type: object
    properties:
      assocType:
        type: string 
      isPrimary:
        type: boolean