Update tf016_tf021.json

[danrfossberg]

feat parameter 21
Heatit z-trm3 thermostats to report kWh, Watt and Volt

Second try to add parameter 21

[zwave-js-assistant]

💡 The pull request title does not match our guidelines 💡

We follow conventional commits, check out the description and examples. This means that the PR title must...

• start with the type of change, e.g. feat:, or fix:
• optionally specify a scope, for example we use config for changes to config files: feat(config):
• contain a description that explains what is being changed, e.g. add a parameter, correct a typo, ...
• and ideally explains what the change affects, e.g. the device (manufacturer, device label, firmware, ...)

The description should use uppercase and lowercase normally, except for the first character which must be lowercase.