Support for kSecClassIdentity and kSecClassCertificate

[sanieldalib]

Hey there, thank you for the amazing work on this project. I am looking for a way to add both certificates and identities into the keychain on macOS using this package. However, this package only seems to include the item classes:

• kSecClassGenericPassword
• kSecClassInternetPassword

Referring to the Apple docs here: https://developer.apple.com/documentation/security/keychain_services/keychain_items/item_class_keys_and_values#1678477 it would be great to include all of these item class values.

[sanieldalib]

It seems that this is addressed in https://github.com/keybase/go-keychain/pull/103. Would be great to get it merged.