Size improvement of credential data serialization

[sosthene-nitrokey]

I think that in many cases (if not most), in PublicKeyCredentialRpEntity, the id and the name field will be the same. Maybe we can skip serializing the name when it is equal to the `id ?

The same applies to PublicKeyCredentialUserEntity, with name and display_name which are likely the same.

I'll have to check on real-world websites to see what the call credential.create with.

[robin-nitrokey]

Some data points:

• GitHub: display name = real name, name = user name
• Microsoft: display name = real name, name = mail address