feat(ble): Read the advertised device name from a file

The user can change the advertised BLE name of their card10 by writing the name in a "device_name.txt" file.

Looks good to me! Thanks for keeping our codebase clean.

However, I'm only a bot - so a human will still have to approve this request.

assigned to @hauke

added 4-BLE label

I am not sure if iOS needs this postfix. @Danukeru

added 6 - Needs Review label

Since it branches on the standard behaviour and is opt-in, this is fine.

However, we have a pending MR for card10.cfg. !215 (merged)

This should be a setting in there. @omniskop

This MR should go through with 1.8 soon after 1.7. :)

This is still only the advertisement name. The service device name is elsewhere, and is still card10.

Is this extra file still needed once there is a centralized configuration?