[rauc][certs] Rework of the custom keyring
The custom keyring is now directly included via the extra search path. In this step, the example keyring was also moved to a new insecure-keys folder. Also see commit 4831fa46.
The custom keyring is now directly included via the extra search path. In this step, the example keyring was also moved to a new insecure-keys folder. Also see commit 4831fa46.