config to use gnome-keyring

gnome-keyring through secret-tool works with a label and pairs of attributes
and values to store a password. I'm already using it to make email account
passwords accessible by msmtp. Setting up getmail to use gnome-keyring would
create a new keyring and the content would be the same as for the previous
keyring. It would be more convenient that getmail also uses the label and the
corresponding pair to retrieve a password from gnome-keyring.