PLT-7633 (E20) Add session idle timeout config setting (#7524)

* Add session idle timeout config setting

* Modify config setting name to SessionIdleTimeoutInMinutes

* Small re-org of if statement

* Merge with latest master

config/default.json

@@ -36,6 +36,7 @@
         "SessionLengthMobileInDays": 30,
         "SessionLengthSSOInDays": 30,
         "SessionCacheInMinutes": 10,
+        "SessionIdleTimeout": 0,
         "WebsocketSecurePort": 443,
         "WebsocketPort": 80,
         "WebserverMode": "gzip",