compose image: Enable specify different places for input and output for the change detection logic

[travier]

Describe the bug

If I want to use the change detection logic in rpm-ostree compose image, I have to let rpm-ostree directly push the results to a container registry, where the previous build is available. I can not ask it to look at the previous build in a registry and then generate a container image stored locally in an ociarchive for exampe.

Reproduction steps

Potential command line for different use cases:

# Look at a registry and store locally
$ rpm-ostree compose image \
     --previous-build docker://registry.io/foo/bar:39 \
     manifest.yaml \
     output.ociarchive

# Look at a local ociarchive and store locally
$ rpm-ostree compose image \
     --previous-build /mnt/compose/foo/stable/bar.ociarchive \
     manifest.yaml \
     output.ociarchive

# Look at a registry and push to another tag
$ rpm-ostree compose image \
     --previous-build docker://registry.io/foo/bar:stable \
     manifest.yaml \
     docker://registry.io/foo/bar:testing

Expected behavior

I'm able to compose a new build that is stored locally, with change detection based on an image stored in a registry.

Actual behavior

If I use the change detection logic pointing to a registry then the resulting build is pushed to the registry in all cases.

Currently:

$ rpm-ostree compose image \
     manifest.yaml \
     [output.ociarchive](docker://registry.io/foo/bar:39)

Will look at the registry for change detection and will push the image to the registry once built.

System details

Latest rpm-ostree on Fedora

Additional information

No response