feat: use github.com/eic/eic-spack as local eic-spack repo

Instead of using the local eic-spack repo, we should use the github eic-spack repo. That centralizes and makes it easier for users to use the same package recipes.

spack/packages/dawn/exec.patch

-diff --git a/DAWN_GUI_menu.header2 b/DAWN_GUI_menu.header2
-index ef35492..7fa067b 100644
---- a/DAWN_GUI_menu.header2
-+++ b/DAWN_GUI_menu.header2
-@@ -1 +1 @@
--exec wish "$0" "$@"
-+exec wish "$0" ${1+"$@"}