Adds a high level persistent storage API

[kaczmarczyck]

Changes the store API to a wider API for data in a persistant way. Joins the attestation store into the regular store, and allows more control over how to special case some of the storage.

The KeyStore had some persistent elements that were moved out, and the crypto-related parts were kept separately.

In some cases, we can consider unifying even more, like the way the PIN hash is stored. To keep the PR smaller, it only implements the general API changes, no updates to specific parts of the API when not necessary.

One planned follow-up is LargeBlob (see the TODO comment).

[ia0]

I didn't check in details, but for the change to be backward compatible, we need to use the same keys and encode the values the same way. From what I've seen so far it seems like it, but just making sure it's conscious.

[ia0]

LGTM
What's the testing strategy?

[kaczmarczyck]

I flashed the PR on hardware, then went through the following tests, mostly storage related:

• webauthn.io: register, then login.
• Go to Chrome settings, delete some credentials, change the PIN, reset the security key.
• A script that writes and then reads a LargeBlob.
• A script that toggles alwaysUv.
• Our configure script to write batch attestation key material.
• webauthn.io again, but using attestation this time.

Then deploy erase_storage, deploy OpenSK again, and another round of the above. Before, it upgraded from the storage as it was right before this PR.