Add country first appearance report

src/django/api/reports/country_first_appearance.sql

@@ -0,0 +1,9 @@
+-- List the ISO country codes where facilities are located sorted by the year
+-- and month that the country first appeared.
+
+SELECT
+  country_code,
+  to_char(min(created_at), 'YYYY-MM') AS created_at
+  FROM api_facility
+GROUP BY country_code
+ORDER BY created_at DESC;