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>

models/issues/comment.go

@@ -114,6 +114,8 @@ const (
 
 	CommentTypePin   // 36 pin Issue
 	CommentTypeUnpin // 37 unpin Issue
+
+	CommentTypeChangeTimeEstimate // 38 Change time estimate
 )
 
 var commentStrings = []string{
@@ -155,6 +157,7 @@ var commentStrings = []string{
 	"pull_cancel_scheduled_merge",
 	"pin",
 	"unpin",
+	"change_time_estimate",
 }
 
 func (t CommentType) String() string {