Display traces side-by-side

[SOF3]

Description

Sometimes Kelemetry's linkers are insufficient to relate two traces or linking is too expensive/large (e.g. linking a leader election object would link all operations that interact with the component). The user can tell us the two traces are related explicitly through a new endpoint e.g. /merge?trace={traceid1}&trace={traceid2} that redirects to a new cached ID.

User story

It is often useful to debug why a controller is not working by comparing its output activity against its leader lease update frequency.