XMPP: private chat response issue

There is an issue in the org.apache.camel.component.xmpp.XmppPrivateChatProducer that prevents responding to XMPP private chat messages. The participant's address is obtained as

String participant = exchange.getIn().getHeader(XmppConstants.TO, String.class);

(see https://github.com/apache/camel/blob/4ad8bcfde6ba931e526cd8680e211a397c6c71e7/components/camel-xmpp/src/main/java/org/apache/camel/component/xmpp/XmppPrivateChatProducer.java#L68)

In case of an incoming message that is the camel instance itself, not the participant. However, from that it creates the outgoing message just as

message.setTo(participant);

(see https://github.com/apache/camel/blob/4ad8bcfde6ba931e526cd8680e211a397c6c71e7/components/camel-xmpp/src/main/java/org/apache/camel/component/xmpp/XmppPrivateChatProducer.java#L82)

Thus, responding to a chat message always results in a message to itself and not the chat's other participant.

I fixed the issue in https://github.com/binfalse/camel/commit/cbada76346fa0aae74128b2b74aa3a834144ea63 by using the endpoint.getParticipant() to set the receipient of the message. Based on that I created a pull request on github: https://github.com/apache/camel/pull/938