Updating python sdk to include group_by at dashboard level (linode#703)

* updating group_by at dashboard level

* reformatting files

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Co-authored-by: Maciej Wilk <mawilk@akamai.com>

Author: mawasthy-lgtm

linode_api4/objects/monitor.py

@@ -278,6 +278,7 @@ class MonitorDashboard(Base):
         "label": Property(),
         "service_type": Property(ServiceType),
         "type": Property(DashboardType),
+        "group_by": Property(),
         "widgets": Property(json_object=DashboardWidget),
         "updated": Property(is_datetime=True),
     }