MM-23935 extend session expiry on user activity (#14275)

* MM-23935  extend session expiry on user activity

- if user types anything before a session expires the session will be extended to now + session length

- ensures new session expiries are not written to DB too frequently

- new session store func for updating session ExpiresAt

- session length defaults for mobile and web/ldap changed from 180 days to 30 days

i18n/en.json

@@ -6910,6 +6910,10 @@
     "id": "store.sql_session.update_device_id.app_error",
     "translation": "Unable to update the device id."
   },
+  {
+    "id": "store.sql_session.update_expires_at.app_error",
+    "translation": "Unable to update expires_at."
+  },
   {
     "id": "store.sql_session.update_last_activity.app_error",
     "translation": "Unable to update the last_activity_at."