feat: import manual maintainers

Signed-off-by: Umberto Sgueglia <usgueglia@contractor.linuxfoundation.org>

Author: ulemons

backend/src/osspckgs/migrations/V1782978597__package_maintainers_ingestion_source.sql

@@ -0,0 +1,2 @@
+ALTER TABLE package_maintainers
+    ADD COLUMN IF NOT EXISTS ingestion_source text;