triage-policies: add a bugbot command for closing bugs

We have labels like needinfo or triage needed but all these labels
require intervention from a privileged user - normal users cannot
set labels on a project.

The only thing users can all do is open/close/re-open bugs. So let's try
to incorporate this into our event flow: if we need something from the
user we ask for it, close the bug and when the user supplies this
information they can re-open it. This means e.g. bugs waiting forever in
triage will not show up as actionable in the issue list.

Since users aren't used to that workflow let's add a bugbot blurb that
explains that we're not really closing the issue, just using that as the
only lever we have available.

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1090>

.triage-policies.yml

@@ -137,6 +137,19 @@ resource_rules:
             [systemd](https://github.com/systemd/systemd/) repository to get that quirk included.
             Please link to the systemd issue here and if the hwdb entry indeed fixed this issue here, please
             remember to close this issue.
+      - name: "Close bug for reopening"
+        conditions:
+          labels:
+            - "bugbot::close"
+          remove_labels:
+            - "bugbot::close"
+          comment: |
+            I'm (temporarily) closing this bug. The bug may not be fixed yet (see any comments above)
+            but unfortunately closing/re-opening is the only action all GitLab users are permitted to
+            do. So we close it, you re-open it when whatever above has been addressed and
+            then we know we need to look at it again. This may happen more than once in this issue but
+            I'll only post this once.
+          status: "close"
       - *close_needinfo
       - *remind_needinfo
       - *help_needed