Perf test viewer

[Sylvain Henry]

Hello everyone,

Since testsuite performance results are stored into Git notes, they are 
more difficult to visualize. At least with values in .T files we could 
see the changes over time, but now increase/decrease are only indicated 
into commit messages (but not necessarily by how much). The only tool we 
have afaik is the perf_notes.py script [1] but it's not very interactive.

So, long story short, I've started another one which is more interactive 
(in the browser). An instance is running on my server: http://hsyl20.fr:4222

It should be updated every 2 hours with newer metrics/commits from CI. 
Sources are here: https://github.com/hsyl20/had

Any feedback/PR is welcome!

Cheers,
Sylvain

[1] 
https://gitlab.haskell.org/ghc/ghc/-/wikis/building/running-tests/performance-tests#comparing-commits