Get project factory ticket to PR time

Takes the median time, in minutes, from the factory picking up a PR's tickets to the PR opening, for PRs a project run produced, by open time, in the requested window (filter[timestamp][gte] to the exclusive filter[timestamp][lt], at most 90 days, the last 7 days when neither is given) and in the window of the same length just before it. A PR's tickets are the issues its producing runs reference. Pickup is the earliest project run that references one of them. The open time is GitHub’s, from webhooks, else when the PR was first linked as produced. A PR with no ticket, or opened before pickup, is left out. medianMinutes is null with no PRs. trackedSince is when the repository’s record of PRs starts, null before its first. series has one point per UTC day that the current window touches, zeros included, and its prs add up to current.