Feature request: Notification in HA payload when no data from the meter

[ArnieO]

Is your feature request related to a problem? Please describe.
Linked to Kamstrup Omnipower HAN port not working

Describe the solution you'd like
In the comments to our article, a user proposes a notification in Home Assistant payload when this issue happens - and this could be expanded to other issues that could require user attention. This sounds like a good idea.

[gskjold]

v2.6 adds a device_class: problem binary sensor and an event entity in the Home Assistant discovery, fed from a new <topic>/event topic. A meter that stops sending raises a han_no_data event and flips the problem sensor, which should be what a notification automation can trigger on.

Test builds are available here: #1270 — it would be good to know whether this covers what you asked for before we finalise v2.6.