Make EncryptedPKM into ASN.1 format with assigned OID

[bitfl0wer]

polyproto offers some HTTP routes to store and retrieve encrypted private key material on/from your home server. This is intended as a backup, for if you lose all of your devices, to not also lose all of your private key material. Since it is technically up to the client to choose, how the private key material will be encrypted (official recommendations for cryptographic algorithms to use will be made), it is a good idea to store some metadata alongside with the encrypted private key material. This metadata should be in a format that is recognizable/parsable by any software through an open specification. The ASN.1 format is already used by polyproto, and it would therefore be a good idea to specify ASN.1 notation for this new type, alongside the JSON notation, which will also be provided.