Store and use seconds for timeline time comments (#25392)

this will allow us to fully localize it later

PS: we can not migrate back as the old value was a one-way conversion


prepare for  #25213

---
*Sponsored by Kithara Software GmbH*

models/issues/tracked_time_test.go

@@ -35,7 +35,7 @@ func TestAddTime(t *testing.T) {
 	assert.Equal(t, int64(3661), tt.Time)
 
 	comment := unittest.AssertExistsAndLoadBean(t, &issues_model.Comment{Type: issues_model.CommentTypeAddTimeManual, PosterID: 3, IssueID: 1})
-	assert.Equal(t, "1 hour 1 minute", comment.Content)
+	assert.Equal(t, "|3661", comment.Content)
 }
 
 func TestGetTrackedTimes(t *testing.T) {