Decrypt ospkg
Adds support for decrypting an OS package which has been encrypted by the "age" (https://github.com/FiloSottile/age) encryption tool, by using "age" as a new, direct dependency.
The feature is enabled if the "/etc/trust_policy/decryption_identities.txt" file exists in the initramfs. The file is used as an "age" identity to decrypt the OS package, unless it is the provisioning OS package.