Changes to Create a sandbox

added the new optional request property persistent

added the new optional request property proxy_config/rules/items/relay_id

added the new optional request property volumes

added the non-success response with the status 403

added the optional property persistent to the response with the 201 status

added the optional property proxy_config/rules/items/relay_id to the response with the 201 status

added the optional property volumes to the response with the 201 status

endpoint added