Add retry with backoff to toDrive

[carderne]

I frequently hit into Google's queue limit (3000), so I've added some code to catch this and use an exponential backoff (starting at 10 minutes) before trying again.

I haven't checked if this is against Google's terms/code of conduct or anything. Very useful for me but no problem if you don't want to add it! :)

[12rambau]

Hi @carderne and sorry for not answering earlier. I took over the maintenance of geetools earlier this year and put lots of effort in refactoring it (working on a proper documentation now).
The new paradigm for the export extension is to remain aligned with the vanilla GEE API i.e. build Task objects that can then be fully managed by the server. In your implementation the client machine needs to remain open during the whole process which is not the direction I (yes I know it's opinionated) I decided to follow.

I will leave this PR on stale and transfer the main idea to a tutorial.

Once it will be moved to the documentation I think I'll close it.

Again thanks a lot for your contribution, if you are still playing with GEE I would be happy to review another improvement proposal and don't hesitate to pass by if you face any bugs.