Describe the feature
Having a more details view of progress, planning of tasks under a milestone using Burndown charts.

Describe the solution you'd like
Burndown charts. It should be easy to implement as Gogs currently already has Milestone support with a due date, issues can already be linked to Milestones. It is only a matter of adding a "start date" on the milestone. Then you can draw two lines in a chart with the dates from start-date to end-date on the x-axis and the amount of open issues on the y-axis. The lines would be as follows:

• one line with an "expected progress" line straight down from number of issues (left) to 0 (right)
• one line with the "actual progress" line with open issues per date

The following screenshot illustrates this feature in Gitlab.com:

Describe alternatives you've considered
Using another tool entirely or partially for this functionality.

Additional context
The Line charts from the open-source project chartsjs (or any other chart library) could be used for this. https://www.chartjs.org/docs/latest/charts/line.html

Firstly, the introduction of this simple feature would be a major benefit. Secondly, an additional feature and chart could be introduced which requires a bit more of work. It could be adding "issue weight" on every issue and calculating not only the burndown of total issues but the apply the weight. Gitlab.com can be used as an example of this feature. Also see the image above in which there are two buttons above the chart: issues and issue weight. The weight should be optional on issues and without a weight defined I'd suggest to weight it simply as 1.

I've requested the same feature at Gitea, here: go-gitea/gitea#10440. Maybe one or both teams could work out some solution that fits both projects, as they are quite similar. Saving some time.