Support locally encrypted file storage

[tyvsmith]

SImple-store should support locally encrypted files to store contents like authorization tokens.

Can take inspiration from https://developer.android.com/reference/androidx/security/crypto/EncryptedSharedPreferences

[kurtisnelson]

It doesn't care what the payload is as long as it is a byte[], so no need for key management to be built in.

[tyvsmith]

Yeah, using byte for storage makes sense. Tentatively, I'd expect a wrapper/util on top to facilitate easy to use APIs for consumers.