Allow separating client id and thing name

[spar-eag]

Is your feature request related to a problem? Please describe.
I have an IoT device with an MQTT client connecting to AWS using the thing name as the client id. I now want to also be able to open a secure tunnel using aws-iot-device-client. Unfortunately, the aws-iot-device-client also uses the thing-name as the client id, causing a duplicate client ID which AWS rejects.

Describe the solution you'd like
Optionally be able to specify which client id to use when connecting to the MQTT broker.

Describe alternatives you've considered
Modify my own application to use a client id different from the thing id. Since I am the author, I can do this, but this might not be possible in all cases, e.g. when using 3rd party software.

[ActoryOu]

Thanks for bringing this into our attention! I'll bring this into team and reply.

[eduelias]

I had that issue and ended up using the "fleet-provision" functionality of the device client to provision "another" thing for it, and using it. Just leaving it here as a work-around if you're willing to do it.