Consider timezone when computing burndown and burnup charts
Continuing the discussion in #213334 (comment 372490939)
Now that our burndown and burnup charts are historically-accurate, we lost the feature of user timezone specific charts.
We could implement this in 2 ways:
- When the user requests the graph data from GraphQL, they include the user's current timezone as one of the arguments.
- Add a timezone setting under a project / group and then use that when viewing milestones in that project / group.
Another option is to keep things as-is and keep everything aggregated by UTC days.