Add sensor.last_seen when homeassistant_legacy_entity_attributes is false

[Enzokot]

Is your feature request related to a problem? Please describe

If I set homeassistant_legacy_entity_attributes to false, then the last_seen and device attributes will be removed from all sensors, that is expected.

Describe the solution you'd like

Please, add sensor.ieeeAddr_last_seen for all devices when homeassistant_legacy_entity_attributes is false and advanced option last_seen is on

Describe alternatives you've considered

I don't know any alternative ways to solve the problem.

Additional context

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 7 days

[andrew-d]

Not stale

[Enzokot]

Keep alive

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 7 days

[Enzokot]

Keep alive

[Koenkk]

What is your use case for this?

[andrew-d]

Speaking personally, I have a notification that goes out periodically that tells me what devices are unreachable, and having the 'last seen' date is helpful to know if it's temporary (i.e. I ignore devices that are only "unavailable" for short periods).

[Koenkk]

@andrew-d for that use case the availability feature fits much better #6281 , you can then create an automation which notifies you when a device becomes unavailable.

[Enzokot]

@Koenkk the last_seen is a quantification. It's impossible to find out how long ago the device stopped sending information.