[shelly] Add totalKWH channels for Shelly Pro 3EM

[JonathanvdGHU]

Added totalKWH channels for Shelly Pro 3EM

Description

I added the missing totalKWH channels for the Shelly Pro 3EM, see #16772. There is also a new totalKWH channel created for the entire device. The channels for reactivewatts are left untouched because I couldn't locate the associated data.

After linking items to the totalKWH channels I noticed that the values only update when you restart OpenHAB at least once.
This also happens for other channels so it's not related to this pull request.

I am btw not really familiar with the code so there are probably some improvements.

[JonathanvdGHU]

@jlaur To be honest, it's a bug fix and an enchancement at the same time. The totalKWH channel for each meter already existed but some work was forgotten and that was why it didn't work.

[lsiepel]

One question, otherwise LGTM
Channels do not seem to be created dynamically, so this would also require thing upgrade instructions.

For future PR's it would be nice to seperate the bug fix and the enhancement. This would make it possible to 1. easy backport bug fixes and 2. list the changes/fixes speerately in the release notes.

[JonathanvdGHU]

One question, otherwise LGTM Channels do not seem to be created dynamically, so this would also require thing upgrade instructions.

For future PR's it would be nice to seperate the bug fix and the enhancement. This would make it possible to 1. easy backport bug fixes and 2. list the changes/fixes speerately in the release notes.

The totalKWH channel for each meter is created when data is written to it. So those are created dynamically. The totalKWH channel for the entire device also pops-up without changing anything other than replacing the current Shelly binding.

I don't mind to creating an extra pull request, so would you prefer I make a new one?