Allow to programatically enable or disable azure.

[zdila]

Calling mgos_sys_config_set_azure_enable(true); doesn't enable azure if it is disabled.

Maybe depends on cesanta/mongoose-os#490

[zdila]

Workaround:

bool mgos_azure_init(void); // not present in mgos_azure.h

void azure_connect() {
  mgos_sys_config_set_azure_enable(true);
  mgos_azure_init();
  mgos_mqtt_global_connect();
}

[rojer]

to be clear: it may work today, but this is not the supported way.
the library needs to be changed to support doing it properly.

[Harvie]

Maybe this workaround can be just added as mgos_azure_enable(bool); call to azure module and when there's new/better way, the code can be modified in azure module, so it will not affect functionality of 3rd party code using it.