support for ledger devices

[brenzi]

We could maintain a fork of
https://github.com/Zondax/ledger-polkadot
Where we just adjust the specifics for our network.

This could be a good thing for multisig governance accounts (multisig, proxy are supported, scheduler not...track this) and for TEER holders too

[brenzi]

there's now a generic solution:
https://forum.polkadot.network/t/new-polkadot-ledger-app/8817