Closes https://github.com/apple/container/issues/1687
The default kernel archive is downloaded from a remote release URL
during first-run setup and via `container system kernel set
--recommended`. Previously, the archive contents were not verified after
download, so integrity depended on HTTPS and the release artifact
remaining unchanged.
This change adds digest verification for kernel archives. The
recommended/default kernel now has pinned digest metadata using an
algorithm-prefixed value such as `sha256:<hex>`. `container system
kernel set --tar` accepts `--digest`; remote tar URLs require it, and
local tar archives can also be verified before unpacking and
installation.
The system config also supports `kernel.digest`, and a custom
`kernel.url` must provide a digest for that archive.
0x4C33