feat: use spack include for central config

spack-environment/concretizer.yaml

+concretizer: 
+  unify: true

spack-environment/dev/spack.yaml

 spack:
+  include: 
+  - ../concretizer.yaml
+  - ../packages.yaml
   specs:
     - acts@21.1.0 +dd4hep +identification +json +tgeo +examples +fatras +geant4 +python
     - actsvg@0.4.26 +examples
@@ -73,11 +76,8 @@ spack:
     - stow@2.3.1
     - tensorflow-lite@2.8.0 -xnnpack
     - xrootd@5.5.1 cxxstd=17 +python +scitokens-cpp
-  concretizer: 
-    unify: true
-  packages:
-    all:
-      compiler: [gcc]
-      variants:
-        +ipo build_type=Release
-  view: /usr/local
+  view:
+    default:
+      root: /usr/local
+      link: all
+      link_type: symlink

spack-environment/packages.yaml

+packages:
+  all:
+    compiler: [gcc]
+    variants:
+      +ipo build_type=Release