Implement binary store format for encrypted clevis data

[anatol]

Currently clevis uses json to store its encrypted data. It also uses base64 encoding a lot. So clevis has a lot of binary->base64->json->base64->... conversions. It adds quite a lot of space and CPU overhead and this could be a problem for services that store/handle a lot of encrypted data.

Try to implement a binary encoding for clevis data using Thrift protocol.