Deprecate spack:concretization over concretizer:unify (#30038)

* Introduce concretizer:unify option to replace spack:concretization

* Deprecate concretization

* Make spack:concretization overrule concretize:unify for now

* Add environment update logic to move from spack:concretization to spack:concretizer:reuse

* Migrate spack:concretization to spack:concretize:unify in all locations

* For new environments make concretizer:unify explicit, so that defaults can be changed in 0.19

share/spack/gitlab/cloud_pipelines/stacks/build_systems/spack.yaml

@@ -1,9 +1,9 @@
 spack:
   view: false
-  concretization: separately
 
   concretizer:
     reuse: false
+    unify: false
 
   config:
     install_tree:

share/spack/gitlab/cloud_pipelines/stacks/data-vis-sdk/spack.yaml

@@ -1,9 +1,9 @@
 spack:
   view: false
-  concretization: separately
 
   concretizer:
     reuse: false
+    unify: false
 
   config:
     install_tree:

share/spack/gitlab/cloud_pipelines/stacks/e4s-mac/spack.yaml

@@ -1,9 +1,9 @@
 spack:
   view: false
-  concretization: separately
 
   concretizer:
     reuse: false
+    unify: false
 
   config:
     concretizer: clingo

share/spack/gitlab/cloud_pipelines/stacks/e4s-on-power/spack.yaml

@@ -1,9 +1,9 @@
 spack:
   view: false
-  concretization: separately
 
   concretizer:
     reuse: false
+    unify: false
 
   config:
     concretizer: clingo

share/spack/gitlab/cloud_pipelines/stacks/e4s/spack.yaml

@@ -1,9 +1,9 @@
 spack:
   view: false
-  concretization: separately
 
   concretizer:
     reuse: false
+    unify: false
 
   config:
     concretizer: clingo

share/spack/gitlab/cloud_pipelines/stacks/radiuss/spack.yaml

@@ -1,9 +1,9 @@
 spack:
-  concretization: separately
   view: false
 
   concretizer:
     reuse: false
+    unify: false
 
   config:
     concretizer: clingo

share/spack/gitlab/cloud_pipelines/stacks/tutorial/spack.yaml

@@ -1,9 +1,9 @@
 spack:
   view: false
-  concretization: separately
 
   concretizer:
     reuse: false
+    unify: false
 
   config:
     install_tree: