Add sharding_key_issue_url for manually backfilled

Changelog: other

db/docs/dependency_list_exports.yml

@@ -17,4 +17,4 @@ desired_sharding_key_migration_job_name: BackfillProjectIdToDependencyListExport
 #   organization_id: organizations
 #
 # A multi-column not-null constraint should be added on these columns.
-
+sharding_key_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/501463

db/docs/security_scans.yml

@@ -12,3 +12,4 @@ gitlab_schema: gitlab_sec
 # because the backfill migration was processed manually.
 # This migration is custom due to data consistency issues and cross-DB backfill.
 desired_sharding_key_migration_job_name: BackfillProjectIdToSecurityScans
+sharding_key_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/501459