Add backlog overview over all next items, regardless of schedule

This is primarily to be used in the weekly review to check all next items for
still being relevant, but can of course be used for other purposes as well.

init.el

@@ -1079,6 +1079,11 @@
                               (org-tags-match-list-sublevels t)
                               (org-agenda-todo-ignore-scheduled t)
                               (org-agenda-sorting-strategy '(priority-down category-up))))))
+                ("B" "Backlog"
+                 ((tags-todo "-HOLD-SOMEWHEN-DATE-PERIODIC/-DONE"
+                             ((org-agenda-overriding-header "Backlog items (next items list without periodic tasks; includes waiting-fors)")
+                              (org-tags-match-list-sublevels t)
+                              (org-agenda-sorting-strategy '(priority-down category-up))))))
                 ("O" "Open, non-periodic TODOs"
                  ((tags-todo "-PERIODIC-SOMEWHEN-REGULAR-HOLD"
                              ((org-agenda-overriding-header "List of open, non-periodic TODO items")