Build-time feature selection: MessageBus support

[iain-anderson]

🚀 Feature Request

Relevant Package [REQUIRED]

This feature request is for... C device SDK

Description [REQUIRED]

Add the ability at build time to configure out/in the different MessageBus implementations, ie Redis, MQTT, NATS (if #428 is implemented)

Describe the solution you'd like

The build script could take a cmdline flag which would set an environment variable, this variable to be read by the CMake files to control source files and link libraries

Describe alternatives you've considered

Have you considered any alternative solutions or workarounds?

[WHE-PC]

Has the new NATS message bus feature been scheduled?
Add NATS MessageBus capability #428