Add parameter to provide a private_key_string, public_key_string, and password_hash_string

[kstine]

Instead of passing in a whole file path, it would be useful to be able to pass the private_key_string, public_key_string, and password_hash_string as a string to CryptoLibrary.

*** Settings ***
Library    CryptoLibrary    private_key_string=%{PRIVATE_KEY}    public_key_string=%{PUBLIC_KEY}    password_hash_string=%{PASSWORD_HASH}

This would enable CryptoLibrary to better integrate with services like Azure Key Vault for example.

Further updating the CryptoLibrary CLI to digest the same strings could be possible. Especially if the CryptoLibrary supported .env files or a static config file.