add history_average_days_per_month to schema

Author: irrationalagent

schemas/telemetry/normandy-login-study/normandy-login-study.4.schema.json

@@ -147,6 +147,12 @@
             "null"
           ]
         },
+        "history_average_days_per_month": {
+          "type": [
+            "number",
+            "null"
+          ]
+        },
         "history_oldest_days_old": {
           "type": [
             "number",

templates/telemetry/normandy-login-study/normandy-login-study.4.schema.json

@@ -93,6 +93,9 @@
         },
         "history_oldest_days_old": {
           "type": ["number", "null"]
+        },
+        "history_average_days_per_month": {
+          "type": ["number", "null"]
         }
       }
     }