Issue time estimate, meaningful time tracking (#23113)

Redesign the time tracker side bar, and add "time estimate" support (in "1d 2m" format)

Closes #23112

---------

Co-authored-by: stuzer05 <stuzer05@gmail.com>
Co-authored-by: Yarden Shoham <hrsi88@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/convert/issue_comment.go

@@ -76,6 +76,11 @@ func ToTimelineComment(ctx context.Context, repo *repo_model.Repository, c *issu
 			// so we check for the "|" delimiter and convert new to legacy format on demand
 			c.Content = util.SecToTime(c.Content[1:])
 		}
+
+		if c.Type == issues_model.CommentTypeChangeTimeEstimate {
+			timeSec, _ := util.ToInt64(c.Content)
+			c.Content = util.TimeEstimateString(timeSec)
+		}
 	}
 
 	comment := &api.TimelineComment{