Add option to not prepend friendly_name to Home Assistant entities

**Describe the problem you have/What new integration you would like**

When adding a friendly_name to a device, this name is displayed in the ESPHome dashboard, improving user friendliness. However, this also prepends the friendly_name to entities in Home Assistant. When using a configuration like:
```yaml
substitutions:
device_name: "Plug Electric Car"

esphome:
friendly_name: ${device_name}

sensor:
- platform: total_daily_energy
name: "${device_name} Energy Today"
power_id: "power"
```
Home Assistant will add the entity sensor.plug_electric_car_plug_electric_car_energy_today, which is unwanted.

It would be nice if we got the option to disable prepending of the friendly_name to any entities in Home Assistant.

**Please describe your use case for this integration and alternatives you've tried:**

Currently two options are available:
- not using friendly name, which makes the ESPHome dashboard look more ugly.
- Not manually prepending the device name to the entities. However, when I have many entities referring to the same packaged file (such as network diagnostics) and these entities do not have a friendly name defined, suddenly the naming of the sensor would just be sensor.wifi_signal for a random device.

**Additional context**

I was a bit unsure if this is an ESPHome feature request or a Home Assistant feature request. If I'm in the wrong category, please let me know.

The request concerns ESPHome friendly_name handling and Home Assistant entity naming; first confirm whether the change belongs in ESPHome or Home Assistant, since the author is unsure. Review the existing friendly_name and entity-naming configuration paths, then define and verify an opt-out that preserves dashboard naming without duplicating the device name in entity IDs.

Written by the indexing model from the issue text.