Passkey stamper crate for testing

[r-n-o]

A lot of integrations depend on passkeys, which are browser/OS controlled. This makes it difficult to test these end-to-end. Let's add a webauthn stamper crate to simulate passkeys. Once we have this up, we can update the "create_sub_organization" example to showcase this, and sign with the software-based passkey as a test.

https://docs.rs/passkey-client/0.4.0/passkey_client/struct.Client.html seems promising!