[Enhancement] Github Authentication

[pchiquit]

The problem

Github Authentication missing.

Environment

• Cryptr version (or git revision) that exhibits the issue: all
• Desktop OS/version used to run Cryptr: all
• Vault version: all

Details

This is one of the only tools that don't seem to require vault superuser access, so it is an ideal tool for an end user to manage it's secrets. My organization has vault configured to use Github authentication, so it would be great if that was one option.

Steps to Reproduce

No Github authenticaiton option on the start menu.