Any appetite for adding a wait all option?

[byrnedo]

Hi,

I've a weird use case where I want fan out to wait for all upstream responses and merge the successful ones.
I forked and modded this plugin, result here: https://github.com/skateco/fanout
Is there any interest in having this functionality in this plugin itself?
If so I could work on an MR given some consensus on how to configure it and things like whether 'race' should be disregarded then.