Selecting a random send service

Hi! I'm the creator of the service fastsi.de, it's a gateway that redirects the user to a random working instance of open-source self-hosted services. This helps users to use self-hosted services, and helps services to distribute the load. It already has send services in it (e.g. https://fastsi.de/send redirects to a random working instance).

At the moment ffsend only uses the send.vis.ee instance, it would be cool to add an included option to get a working send instance via fastside and use it to upload a file.

This could be implemented via a separate flag, for example -r (--random-instance). I am willing to help implement this functionality if you approve this feature.

Of course, it's just as important to provide the ability to use a fastside instance other than the official one.

The advantages I see:

• The load on send.vis.ee will be reduced, distributed to other instances
• Increase decentralization and fault tolerance.

Cons I see in this approach:

• Different instances have different limitations, because of this some instances will not be able to upload a large file/set a large availability expiration time/large number of file downloads.
• Some instances provide poor upload/download speed.