Update keychain package

- improves compatibility with OMF
- optimises loading
- allows customising options
- fixes case where SHELL var is not set

packages/keychain

 type = plugin
-repository = https://github.com/pkg-gretel/pkg-keychain
+repository = https://github.com/jitakirin/pkg-keychain.git
+maintainer = jitakirin <jitakirin@gmail.com>
+description = Keychain helps you manage SSH and GPG keys