start using the icebox queue

Without it, the "Open" queue has a lot of junk and new tickets get
lost in the noise. By moving most of that junk in the Icebox queue,
new tickets immediately pop up in the Open queue and can be properly triaged.

policy/tpa-rfc-5-gitlab.md

@@ -56,11 +56,12 @@ Instead, it is suggested we adopt the [Kanban][] development strategy
 which is implemented in GitLab as [issue boards](https://docs.gitlab.com/ee/user/project/issue_board.html). 
 
 Issues first land into a "triage" queue (`Open`), then get assigned to
-a specific milestone as the ticket gets planned. We use the `Backlog`,
+a specific milestone as the ticket gets planned. We use the `Icebox`, `Backlog`,
 `Next`, and `Doing` of the global "TPO" group board labels. With the
 `Open` and `Closed` list, this gives us the following policy:
 
- * `Open`: untriaged ticket, "ice box"
+ * `Open`: untriaged ticket
+ * `Icebox`: ticket that is stalled, but triaged
  * `Backlog`: planned work
  * `Next`: work to be done in the next iteration or "sprint"
    (e.g. currently a month)
@@ -74,7 +75,10 @@ this policy.
 Priority of items in the lists are determined by the *order* of items
 in the stack. Tickets should *not* stay in the `Next` or `Doing` lists
 forever and should instead actively be closed or moved back into the
-`Open` or `Backlog` board.
+`Icebox` or `Backlog` board. Tickets should *not* be moved back to the
+`Open` board once they have been triaged. The `Open` board should
+ideally be always empty: as soon as a ticket is there, it should be
+processed into some other queue.
 
 [Kanban]: https://en.wikipedia.org/wiki/Kanban_(development)