warn about removal of deprecated format strings (#34101)

* warn about removal of deprecated format strings

Co-authored-by: becker33 <becker33@users.noreply.github.com>

etc/spack/defaults/config.yaml

@@ -19,7 +19,7 @@ config:
   install_tree:
     root: $spack/opt/spack
     projections:
-      all: "${ARCHITECTURE}/${COMPILERNAME}-${COMPILERVER}/${PACKAGE}-${VERSION}-${HASH}"
+      all: "{architecture}/{compiler.name}-{compiler.version}/{name}-{version}-{hash}"
     # install_tree can include an optional padded length (int or boolean)
     # default is False (do not pad)
     # if padded_length is True, Spack will pad as close to the system max path
@@ -219,4 +219,3 @@ config:
   flags:
     # Whether to keep -Werror flags active in package builds.
     keep_werror: 'none'
-