Add support for OS keyrings

[warhodes-dev]

Ideally this application will support OS keyring features like Windows Credentials Manager, macOS Keychain, or Linux secret-service through keyring-rs.

Bizarrely, this feature is not widely supported on headless Linux systems (which, hello, is exactly who would use a tui client). For example some discussion here regarding secret-service support in WSL. (See also: google "secret-tool on headless Linux system").

The plan is:

1. Support OS Keyring when possible
2. Support something like .netrc if faster authentication is desired
3. Manual authentication by default as a fallback