Add traversal_path to siphon_knowledge_graph_enabled_namespaces and siphon_namespace_details

What does this MR do and why?

• Remove old siphon_knowledge_graph_enabled_namespaces table and recreate with traversal_path column
• Remove old siphon_namespace_details table and recreate with traversal_path column

References

Resolves gitlab-org/orbit/knowledge-graph#503 (closed)

How to set up and validate locally

1. Run the ClickHouse migration:

   bundle exec rake gitlab:clickhouse:migrate:main

2. Verify the column exists:

   clickhouse client --port 9001 --database gitlab_clickhouse_development --query "DESCRIBE siphon_knowledge_graph_enabled_namespaces FORMAT PrettyCompact"
   clickhouse client --port 9001 --database gitlab_clickhouse_development --query "DESCRIBE siphon_namespace_details FORMAT PrettyCompact"

3. Confirm traversal_path shows up with the dictGetOrDefault default expression.

MR acceptance checklist

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