Optional prefix for Home Assistant autodiscovery entity ID
Allow adding an optional prefix that will be added to the generated entities ID via autodiscovery in HomeAssistant.

## Feature description
PAI generates alot of entities so it's a good idea to have a way to quickly identify them in different scenarios.
eg.: exclude most of them from recorder (easily done if they are prefixed) and only include a few that are of interest.

Moreover, some of the current entities have IDs that do not hint at all to the PAI integration.
See: `binary_sensor.system_troubles_*` or `sensor.system_power_*`.
