Add `@bors perf` command or similar

The typical workflow when having to get perf data for a commit is

@bors try

(wait until bors posts that it is done)

@rust-timer build SHA

(wait until that is done)

It would be great if bors would have a command like perf, that would work basically exactly the same as try, except that the “try build done” message would invoke the rust-timer bot the same way that we currently have to do manually (yay, bots calling bots). So, no human interaction should be needed, after doing @bors perf, until the final perf results are in.

Cc @Mark-Simulacrum

[pietroalbini]

It would probably be better to add this to rust-timer itself?

[Mark-Simulacrum]

I don’t think we can do better than that personally (or should, perhaps). So closing.