Create T-all zulip user group

This is needed to configure the infra announcement channel so the zulip
user group membership is synced automatically with project team
membership.

This notably does not include working groups, project groups, or marker
teams. The cloud-compute marker team will need its own zulip user group
in a follow-up.

Author: jieyouxu

teams/all.toml

@@ -31,3 +31,6 @@ extra-emails = [
 
 [[discord-roles]]
 name = "WGs and Teams"
+
+[[zulip-groups]]
+name = "T-all"