Signer: update to ledgerwallet.0.3.0 API

Context

During the development of the Tezos app on Ledger Nano devices or their integration in octez, it's more convenient to use the (Speculos emulator)[https://developers.ledger.com/docs/speculos/introduction/] than to actually get a device and upload an experimental app on it. Further more, having a simulator opens the door to integration of tests of Ledger support in the CI. This MR enables it.

Manually testing the MR

• (Not that trivial) Launch speculos with the (tezos app)[https://github.com/LedgerHQ/app-tezos] (ressources to compile on https://developers.ledger.com/docs/nano-app/build/)
• LEDGER_PROXY_PORT=9999 octez-client list connected ledgers

Depends on opam-repository!377 (merged)

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR