Step template package reference bug fix

• Support the certificate variable type (still doesn't clone certs, but supports the variable type now)
• Fixes a bug where step templates packages weren't getting cloned correctly with the built-in feed
• Fixes a bug where the azure cloner attempted to create a GUID object rather than a GUID string
• Will now show 401 unauthorized error instead of unable to read response stream error
• Tested against a 2020.5.x instance