Track time for specs changed in MRs having "rspec profiling" label

Although overall improvements are visible in the "overall" table/chart, it would be handy to see how timings have changed in all spec files which have been changed in MRs labeled rspec profiling.

So the table could display something like this:

file_name                                                            | time (week 1)  | time (week 2)  | ... |  time (week X)
./spec/services/notification_service_spec.rb (list of links to MRs)  | 100            | 90             | ... | 92