Use libsodium's defined asymmetric encryption scheme instead of RSA

[ymarcus93]

Currently, we use the RSA library provided by the standard library in Go. However, the Callisto paper mentions using libsodium for doing asymmetric encryption with the DLOCs and LOCs. Details of the scheme used can be found here: https://libsodium.gitbook.io/doc/public-key_cryptography/authenticated_encryption

Transitioning to this scheme would require instantiating a public DH value for the client, as well as the DLOCs and LOCs.

[ymarcus93]

Alternatively, use the sealed box approach so that Client does not need to manage private DH secrets