+act #13004 Adding TailChopping router

Initial implementation + test for #13004
Does it look ok, or some generalisation with ScatterGatherFirstCompletedRouter should be made instead? 
I will update doc when final solution will appear.
Ok, so thoughts about this.

We'll want to make the magical `2` configurable.

* make the 2 here configurable.
* make the default value be `1`, if someone wants more cycles they will opt-in

In the mean time, i'm thinking on removing the atomic :)