Need timestamp in the template

[zhongys-c8y]

The current template only supports replacing the value of one single variable. In some scenarios, it is also necessary to provide the timestamp for the data to indicate the time it was retrieved.

• Goal: When the json template includes timestamp fragment, the plugin should be able to set it to the time when the plugin reads the value from the device.

[reubenmiller]

Closed as the timestamp is now added by default. #47