feat: add a default SQL view for easy Grafana querying (#1289)

search-service/src/main/resources/db/migration/V0_44__add_view_for_grafana_querying.sql

@@ -0,0 +1,11 @@
+CREATE VIEW flattened_entities_attributes_values AS (
+    SELECT entity_payload.entity_id,
+       TRIM(JSONB_PATH_QUERY_FIRST(entity_payload.payload, '$."https://schema.org/name"[0]."https://uri.etsi.org/ngsi-ld/hasValue"[0]."@value"')::TEXT, '"') AS "entity_name",
+       attribute_name,
+       dataset_id,
+       time,
+       measured_value AS value
+    FROM attribute_instance
+    LEFT JOIN temporal_entity_attribute ON temporal_entity_attribute.id = attribute_instance.temporal_entity_attribute
+    LEFT JOIN entity_payload ON entity_payload.entity_id = temporal_entity_attribute.entity_id
+);