Prefix `device_name` to `entity_name`

[webash]

Since Home Assistant builds the entity_id from the name property of an HA discovery packet, this ensures entity_ids are more specific than just apparent_power.

When displaying the entities, particularly on the device page, Home Assistant will omit the device name part of the string, because it will match the device name and that's how HA device-->entity hierarchy is maintained in the display names.

Having descriptive/specific entity_id is useful when only being able to glance at the entity_id in a config. Similarly, the entity name containing the device name means that if you update the device name, all the entity (display) names of that device also update to match.

Specific name and id make auto-complete/entity-only views clearer when trying to pick something like a reactive_power amongst a list of multiple of them; because now the entity ID or display name tell you which device without having to look it up separately.

How will this affect existing users?

• Users who do not update their config.json: Nothing The config item discovery_entityname_prefix_with_devicename will be null because it won't exist, so it won't update the entity_name and it will stay the same as it was in previous versions.
• Users who DO update their config.json: Existing entities in HA will have the display name updated to include the device name, but the entity_id will not update due to this potentially being a breaking change.

All new users, or any existing users who configure the option AND delete their existing Home Assistant objects will see the intended behaviour, with all entity_id having the device id specified in it.

Any existing users who want this change, but are not wishing to lose the history of objects already added can update the entity_id for each entity manually before or after adding "discovery_entityname_prefix_with_devicename": true to their config file.

[webash]

Ugh, it appears 2023.8 of Home Assistant is changing the behaviour of this. I haven't yet updated, so I'll do that shortly and figure out whether this is still required. Probably isn't.

[webash]

Yep; Home Assistant 2023.8 now finally configures the initial entity_id of an entity linked (via identifier or connection) to a device with the device name included, so that you don't end up with binary_sensor.motion as the entity_id for an MQTT entity configured with only the entity_name of motion. Now it will finally configure that at as binary_sensor.device_name_motion.

So this workaround that I added in this PR is no longer required for anyone on 2023.8 onwards.

I'll leave it open for now, but I'm guessing there isn't much point in adding it

[Achronite]

I used to have the device_name prefixing the entity names, but had to change it due to the changes in naming standards (enforced in HA 2023.8). See #34. So, sorry, I'm going to have to reject this pull request as it is.