Add a way to add a recovery signers to the example passkey app

[mmv08]

Currently, the example application is missing a way to add a recovery signer to prevent passkeys from being a single point of failure.

The goal of this issue is to provide a way to add a recovery signer to the account AFTER it has been created. Creating an account with a recovery signer is out of scope until #372 is figured out

[nlordell]

Implemented sometime in the past.