Support for low power mode and keep accessory power on

[jeffborg]

I'm just a user of the home assistant tesla fleet addon, But I'm aware that keep accessory power & low power mode are available commands.

I have modified the tesla addon without modifying this library https://github.com/jeffborg/tesla-fleet-extra but this is calling a private method to do the signed commands directly

there are 2 issues I see

1. need to add the on/off toggles for each function
2. somehow for state of these 2 toggles it's seems this is part of some base64 encoded protocol buffer data and it's not in the json