lang/org: use org-attach instead of custom system

- Adds more keys under `<localleader> a`
- Reconfigures org-download to use org-attach system
- Make org-id-track-globally = t a global default now (not just for
  org-brain)
- Renamed +org-init-centralized-attachments-h to +org-init-attachments-h
- org-attach-store-link-p = t (stores a link to an attachment when it is
  attached)
- org-attach-use-inheritance = t (inherit attachment properties from
  parent nodes)

modules/lang/org/contrib/brain.el

@@ -4,9 +4,7 @@
 (use-package! org-brain
   :defer t
   :init
-  (setq org-id-track-globally t
-        org-id-locations-file (concat doom-etc-dir "org-id-locations")
-        org-brain-visualize-default-choices 'all
+  (setq org-brain-visualize-default-choices 'all
         org-brain-title-max-length 24
         org-brain-include-file-entries nil
         org-brain-file-entries-use-title nil)