For OCI remotes, the existing sideload repository system doesn't
work: identity for OCI remotes is done by manifest digest (disguised
as a fake commit ID internally), instead of by ostree commit, so
we have no way of knowing whether a sideloaded image matches the
summary.
Allow specifying a new form of sideload repository with:
--sideload-repo=oci:<path>
The desired use case for this is preinstalling Flatpaks during OS
install, and for this, binding the entire repository to a single
collection ID is both inconvenient and not useful, so OCI sideload
repostories don't have a defined collection ID - they just apply to
all OCI remotes. (And, because of this, they are restricted to
the command line.)
3e9e68cc5d