func GoogleJSONFile(projectID, cluster, filename string) Option {
	return func(c *config) {
		c.googleJSONFile = filename
		c.projectID = projectID
		c.cluster = cluster
	}
}
GoogleJSONFile configures Publisher & Subscriber for Google Cloud Pub/Sub auth using JSON filename
package pubsub
import "github.com/febytanzil/gobroker"
type Option func(c *config)
type config struct {
	serverURL string
	vHost string
	googleAppCred []byte
	googleJSONFile string
	projectID string
	cluster string
	retry int
	codec gobroker.Codec
	contentType string
}
func RabbitMQAMQP(server, vHost string) Option {
	return func(c *config) {
		c.serverURL = server
		c.vHost = vHost
	}
}
func GoogleJSON(projectID, cluster string, cred []byte) Option {
	return func(c *config) {
		c.googleAppCred = cred
		c.projectID = projectID
		c.cluster = cluster
	}
}