JSON serialization of ImageConfiguration is non-deterministic

[allisonkarlitskaya]

Sometimes you get

        "Labels": {
            "maintainer": "[email protected]",
            "containers.composefs.fsverity": "6c8fb1443b014c416e3ebddd8c75307182661f9093f83d3700499e7601aecb61"
        }

sometimes you get

        "Labels": {
            "containers.composefs.fsverity": "6c8fb1443b014c416e3ebddd8c75307182661f9093f83d3700499e7601aecb61",
            "maintainer": "[email protected]"
        }

ie: probably we ought to sort by key before writing the JSON. Or maybe use an inherently-sorted type. Or at least ordered.

[cgwalters]

In ocidir we use https://docs.rs/olpc-cjson/latest/olpc_cjson/ by default (ref code) but... containers/ocidir-rs#10