Is your feature request related to a problem or challenge? Please describe what you are trying to do.

All ObjectStores apart from S3 support conditional predicates on PUT. This is incredibly useful for building transactions on top of object storage.

Describe the solution you'd like

I would like to propose a new put_opts call, in a similar vein to the existing get_opts. This would take a PutOptions similar to GetOptions and containing these predicates.

Describe alternatives you've considered

Additional context

#145 would likely also benefit from a put_opts call