consider adding MTI crypto suites

[Sakurann]

There has been feedback from EUDIW that having a small list of MTI (mandatory to implement) crypto suites for multiple things would greatly help for interoperability. Below is probably a least controversial list..?

Issuer Signatures:

• ECDSA using secp256r1 and SHA-256

Key binding/presentation and Verifier Signatures:

• ECDSA using secp256r1 and SHA-256

Encryption (if needed):

• AES-256-GCM

Hashing:

• SHA-256

[andprian]

This list looks reasonable.

[c2bo]

For encryption, it might make sense to mandate support for AES-128-GCM as well. Same Security Strength as ECDSA + P256 and most references I've seen in the past mandate support for AES-128-GCM and recommend AES-256-GCM (e.g., TLS 1.3 https://www.rfc-editor.org/rfc/rfc8446.html#section-9.1).