Use secureString for secret ARM template parameter values

Noticed this while going through the docs -- I have also removed unnecessary default parameter values which will only cause confusion if you mistakenly do not pass the right parameter from the command line.

Author: jackhorton

articles/container-apps/background-processing.md

@@ -163,12 +163,10 @@ Create a file named *queue.json* and paste the following configuration code into
             "type": "String"
         },
         "environment_name": {
-            "defaultValue": "",
             "type": "String"
         },
         "queueconnection": {
-            "defaultValue": "",
-            "type": "String"
+            "type": "secureString"
         }
     },
     "variables": {},