Update CustomSensorFilter to filter timestamp based on lte (#99)

Author: esirK

sensorsafrica/api/v2/filters.py

@@ -1,6 +1,15 @@
+from django.db import models
+import django_filters
 from feinstaub.sensors.views import SensorFilter
 
 class CustomSensorFilter(SensorFilter):
     class Meta(SensorFilter.Meta):
-        # Pick the fields already defined and add the location__country field
-        fields = {**SensorFilter.Meta.fields, **{'location__country': ['exact']}}
+        fields = {"sensor": ["exact"],
+                    "location__country": ['exact'],
+                    "timestamp": ("gte", "lte"),
+                }
+        filter_overrides = {
+            models.DateTimeField: {
+                'filter_class': django_filters.IsoDateTimeFilter,
+            },
+        }