fix(wpcarro/emacs): Ensure debug-on-error is globally set

I'm still a bit confused about the nuances between the myriad of ways to handle
variables in Emacs...

- `setq`
- `setq-default`
- `setq-local`
- `defvar`
- `defcustom`
- `defconst`
- `customize-set-variable`
- `make-local-variable`
- `make-variable-buffer-local`
- `kill-local-variable`

...but after running some experiments, this triggers the Emacs debugger when an
error is encountered (e.g. either *in* `init.el` or another package that is
evaluated during `init.el`'s evaluation).

Change-Id: I00d543735b1d816462ba18bad23867865d7af80e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4812
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/emacs/.emacs.d/init.el

@@ -1,4 +1,5 @@
 ;; load order is intentional
+(setq-default debug-on-error t)
 (require 'wpc-package)
 (require 'wpc-misc)
 (require 'ssh)