Fix getRetries CTAP 2.0 / 2.1 behavior

[msirringhaus]

For some reason I have not tried my Nitrokey3 with this lib before and noticed some issues.

1. The GetInfo response contained already some 2.2 members, which made serde unhappy, so I added all of the 2.2 fields (although, we should ignore all unknown keys, but serde_indexed doesn't seem to have this functionality)
2. getRetries requires the PIN protocol in CTAP 2.0, but not anymore in 2.1.
3. Sadly, my NK3 still error-ed out with MissingParameter, because it has a bug and reports full 2.1 support, but still requires the PIN protocol (see here). So I changed the hard error into a soft error, as the displaying of the retry counter is optional anyways.

[AlfioEmanueleFresta]

Thanks @msirringhaus! Good point on ignoring unknown fields, IMO this is crucial to do before our first release, allowing forward-compat with future spec versions. Created #66.