kata-deploy: helm: Add overlooked INSTALLATION_PREFIX env var

At the same time that INSTALLATION_PREFIX was added, I was working on
the helm changes to properly do the cleanup / deletion when it's
removed.  However, I missed adding the INSTALLATION_PREFIX env var
there. which I'm doing now.

Signed-off-by: Fabiano Fidêncio <fabiano@fidencio.org>

tools/packaging/kata-deploy/helm-chart/kata-deploy/templates/post-delete-job.yaml

@@ -90,6 +90,8 @@ spec:
           value: {{ .Values.env.pullTypeMapping | quote }}
         - name: HELM_POST_DELETE_HOOK
           value: "true"
+        - name: INSTALLATION_PREFIX
+          value: {{ .Values.env.installationPrefix | quote }}
 {{- with .Values.env.hostOS }}
         - name: HOST_OS
           value: {{ . | quote }}