Expose getPublickey method in the SDK

[sameersubudhi]

Description

Please expose the getPublickey in the lisk-cryptography

Motivation

Currently, the SDK doesn't default export a utility to extract the account publicKey from the account privateKey.
As the utility is already implemented, it would be nice to expose and make it available for use outside the SDK.

Additional Information

Current usage:

import {getPublicKey} from "@liskhq/lisk-cryptography/dist-node/nacl"