Global default flytefile downloader

[pingsutw]

Tracking issue

NA

Why are the changes needed?

downloader is only picklable if they are defined at the top-level of a module. https://docs.python.org/3/library/pickle.html#what-can-be-pickled-and-unpickled

What changes were proposed in this pull request?

move it to global

How was this patch tested?

Setup process

Screenshots

Check all the applicable boxes

• [ ] I updated the documentation accordingly.
• [ ] All new and existing tests passed.
• [ ] All commits are signed-off.

Related PRs

Docs link