Allow automatic saving of USD stage rather than serialization

[alekamca]

Quoted from #53 (comment)

Yes, we also considered this, and there's a lot to like about storing this data in a side-car file that can be accessed outside of Maya. It'll take some wrangling to make sure that callbacks are always firing at the right moments so that data is not lost. Xgen pre-2017 is a good example of how this approach can go wrong, but I think it's a solvable problem and we'd love to see this become an option.

Our maya pipeline is built on sidecar files with quite a bit of bookkeeping to handle importing and referencing, so maybe we can look into how to contribute back some of this work in order to support this workflow.

[dbaz]

Hey @alekamca, is there anything you needed from us(Animal Logic) for this issue?

[alekamca]

@dbaz I think the biggest thing is looking for direction on how to do this in a way that doesn't disrupt existing workflows. The nice thing about serialization is that it protects you from upstream changes. Always syncing with the sidecar files means you will need a proper sandboxing system and file resolver. This isn't an easy change to take on, but at the same time, supporting multiple workflows is also difficult.