[WIP] parse OCI deployment status

[jbtrystram]

When the deployment is an OCI image, the base_commit_meta field contains serialized JSON.

So the values in this map can either be:
- Regular OSTree case: a JSON object
- OCI case : a string containing a serialized JSON object

In the OCI case, simply deserialize the strings before passing them to serde, when necessary.

See #5196

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
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[cgwalters]

A lot of discussion in #5196

[cgwalters]

The json-in-json we have now is obviously silly and unergonomic, and I am not opposed to trying to just change it. However, it is possible that something is parsing it as is today and there's some risk of breakage from that.

Per discussion in the issue, my inclination is basically to try to fix this a different way for now - ideally one that ends up using bootc and leave rpm-ostree as is.

[jlebon]

Per discussion in the issue, my inclination is basically to try to fix this a different way for now - ideally one that ends up using bootc and leave rpm-ostree as is.

To be able to always query that info from bootc, I think it also needs to support fishing it out of the OSTree commit even if there are layered packages.

Anyway, feels weird to me to even have these keys in the --json output. We should probably filter it out like we do the rpmdb. OTOH, that would also technically be an API break at this point.

I guess forking ostree container image metadata is OK, though Zincati could also just re-deserialized the string itself since that's already in the rpm-ostree status output it captures. It's ugly but that'll also get cleaned up once we move to bootc.

[cgwalters]

I think it'd be easier (and more reliable) to just add a method to this get_base_manifest(&self) -> Result<Option<oci_spec::image::ImageManifest>> that directly accesses the expected key, instead of trying to heuristically parse every single metadata key as json.