Add CopyOptions

[tustvold]

Largely a placeholder as I lack a motivating use-case for this functionality

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

Following #4984 we now have put_opts and get_opts. It makes sense to expose the conditional copy semantics of many stores, in particular:

• Source preconditions, such as If-Match
• Destination preconditions, e.g. PutMode

Describe the solution you'd like

I would like a copy_opts method, which is called by default implementations of copy and copy_if_not_exists, and supports the common preconditions supported by object stores.

Describe alternatives you've considered

Additional context

[tustvold]

This might also provide a mechanism to support cross-bucket copies, which currently are not supported