Extend system.file with file.decode module

Prod-related: PROD-27795(PROD:27795)

Change-Id: I58e15c7c22934da9626fa9ad4de4295956b9daf9
diff --git a/tests/pillar/system.sls b/tests/pillar/system.sls
index 73448aa..d5a953e 100644
--- a/tests/pillar/system.sls
+++ b/tests/pillar/system.sls
@@ -34,6 +34,10 @@
         name: /tmp/test3.txt
         source: salt://linux/files/test/file_template.jinja
         template: jinja
+      test4:
+        decode: True
+        name: /tmp/test4.txt
+        encoded_data: dGVzdDQK
     apt:
       preferences:
         enabled: true