Add credential protection policy and large blob support

[jeriox]

We needed support for large blobs and credential protection policy in our project, which py_webauthn didn't provide. We added the appropriate structs and options to genereate_registration_options which worked fine for us.

closes #127

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[MasterKale]

I neglected to thank you for submitting this PR: thank you! I've been meaning to sit down and think about extension support with a bit more abstract API that wouldn't require you to know all of the values for a given extension.

For example, why not have an optional require_large_blob_support: bool argument to generate_registration_options(), since the only option in AuthenticationExtensionsLargeBlobInputs that's valid for registration is support? Technically require_large_blob_support=False would do the same thing as setting support: "preferred" because the spec itself states:

Otherwise (i.e. support is absent or has the value preferred):

So there's no need to even include the value if you're not going to set it to "required".

And for authentication you can specify either read or write, but not both. Therefore I could see adding a write_large_blob: Optional[bytes] = None and read_large_blog: bool = False to generate_authentication_options(), and error out when both are set, so that the developer using the method doesn't need to be aware of the intricacies of the spec - we can remove most of the footguns for them.

These are the angles from which I was going to approach adding support for extensions like largeBlob. Since you're interested in the feature, though, I'm curious to hear what you think about this approach.

[MasterKale]

Closing for now due to inactivity