Allow output of Syft JSON format in multiple schema version

What would you like to be added:

Right now the Syft JSON format schema version is hard-coded (seems to be to the latest version). When you bump to a newer version of syft, it will start outputting the new format. It would be helpful if you could control the Syft JSON schema version used for output, like syft package --output json-v2. I think it would be sufficient to control it at the major version level.

Why is this needed:

Well, it's nice to keep on the latest version of the syft tool for bug fixes and scanner improvements but when the output format changes it can take time to adjust the tools that are consuming the output to read the new format.

I can understand if it's not possible to support all major versions for all of time, but supporting the most recent two or three (depending on how quickly the increment) would help provide time to plan and update tools consuming the output.

Additional context:

I'm not sure this would be something necessary when syft hits 1.0, as I'd assume that means the schema changes will be non-breaking, but in the meantime, it would help to have a feature like this so that it can ease the migrations between schemas.

I wouldn't be opposed to alternative solutions either, so this could perhaps be a question and not an enhancement. Like if for example, I could somehow recompile and have it use a different JSON schema version but still get other updates/fixes.

Thanks

The issue names no files, tests, or entry points. Start by locating Syft's JSON output and schema-version handling, then determine how existing output formats are registered and tested. Done means the CLI can select supported major JSON schema versions while preserving current output behavior.