fix: add missing datasource definition for country_mapping_ds (#3393)

Signed-off-by: Raúl Santos <4837+borfast@users.noreply.github.com>

Author: borfast

services/libs/tinybird/datasources/datasources/country_mapping_ds.datasource

@@ -0,0 +1,8 @@
+SCHEMA >
+    `country` String,
+    `flag` String,
+    `country_code` String,
+    `timezone_offset` Int16
+
+ENGINE MergeTree
+ENGINE_SORTING_KEY flag, country_code, timezone_offset