Adding header on message

[toninho09]

I changed the message to contain the headers

only work if set the client.Version to 0.11+ on samara client

Example processor with config.Version 2.2.0

p, err := goka.NewProcessor(
	brokers,
	g,
	goka.WithConsumerBuilder(func(brokers []string, group, clientID string) (consumer kafka.Consumer, err error) {
		config := kafka.NewConfig()
		config.ClientID = clientID
		config.Version = sarama.V2_2_0_0
		return kafka.NewSaramaConsumer(brokers, group, config)
	}),
)

Your can get the headers from context with ctx.Headers()

[db7]

That's nice! LGTM @frairon