Provide customizable websocket upgrade request parameters

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- [x ] Bug exists Release Version 1.1.1 ( Master Branch)
- [ ] Bug exists in Snapshot Version 1.1.2-SNAPSHOT (Develop Branch)

If this is a bug regarding the Android Service, please raise the bug here instead: https://github.com/eclipse/paho.mqtt.android/issues/new

Websocket upgrade request as per the spec - https://tools.ietf.org/html/rfc6455#section-1.3 can be customised. For eg -
GET HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Protocol:
Sec-WebSocket-Version: 13

Please provide options to customize them.