Compatibility with the MultiQC module is broken as of bustools 0.43.1

[jdidion]

Please see the issue here: MultiQC/MultiQC#3049

It would be appreciated if you could consider downstream tools when you make breaking changes to bustools' public API (yes, JSON keys in the metrics file are part of the public API).

Could you add an option for backward compatibility, e.g., --use-legacy-json-keys?

Thanks