Ability to change the time period when calculating TaT

[remiolsen]

Right now, 30 days is hard-coded in both front-end and back-end. This doesn't really make sense for holidays, when there is very little activity in the lab. 90th percentile when N=5 projects for instance.

One suggestion is to hardcode longer retrospectives (60 or 90 days) in january and august. Needs to be decided.

[ewels]

Alternatively, we could consider the last n projects? I'd rather avoid changing the limits as I think it's a bit confusing.

[remiolsen]

For reference this is what the needle is representing