Add category "Opened and Closed Issues" to activity overview

[MGChecker]

Currently, the gitea activity overview does not allow to calculate how the amount of open issues has changed over a certain timeframe, since issues that have been opened and closed in this time are only counted as closed issues.

This could be fixed by either listing these issues as new and as closed, or by introducing a third category for those. For PRs, it is basically the same issue.

[lafriks]

Yeah, probably new category would be most useful

[stale]

This issue has been automatically marked as stale because it has not had recent activity. I am here to help clear issues left open even if solved or waiting for more insight. This issue will be closed if no further activity occurs during the next 2 weeks. If the issue is still valid just add a comment to keep it alive. Thank you for your contributions.

[MGChecker]

I would still really appreciate for this to be done.

[tmnvanderberg]

I nobody objects, I'll see how easy it is to add a third category

[lunny]

Closed by #31776