Define JOSE and/or COSE bindings for HDK

[sander]

For interoperable representation of HDK key handles and paths (including initial seed salt), we may need to define:

• JOSE binding for use in e.g. OpenID4VCI
• COSE binding for use in e.g. FIDO2 authenticators

Also, a WSCA may use either binding in internal representation and over the Secure Cryptographic Interface.

[sander]

Possibly also a string binding for use as key alias in https://github.com/cleverbase/wallet-secure-crypto-commons/blob/main/sci/README.md, for example:

ascii(<key_id>) || "/0/2/" || base64url(<kh>) || "/1"

[sander]

Comment regarding the HDK key alias format in -06: now aliases could accidentally look like base64-encoded strings. We may add hdk: or something else to guarantee that no alias can be successfully parsed as base64, to catch implementation errors early.