Support user specifying syft-json version

[wagoodman]

Like we've done with other formats, we'd like to be able to have the user be able to select the syft-json version on the CLI:

syft myimage:latest -o json@16

This way we can add new schemas with breaking changes that are opt in, not the default, thus allows us to iterate on core format models without forcing a syft v2 build:

syft myimage:latest -o json@17-dev