Add traversal_ids and archived to vulnerability_statistics

What does this MR do and why?

Add archived and traversal_ids columns to vulnerability_statistics table to resolve cross-database joins in ProjectGrades.grades_for (when the vulnerable is a group) and EE::Group#vulnerability_scanners.

These new columns make it possible to query vulnerability statistics and other tables of the gitlab_sec schema for all the projects a large group and its subgroup, and without joining the projects and namespaces tables (of the main schema).

See proposal and implementation plan of the related issue (#512592 (closed)).

References

This is similar to Add `archived` and `traversal_ids` columns to `... (!143104 - merged) but the goal is different. Instead of de-normalizing archived and traversal_ids for performance, we do it to remove cross-database joins (involving gitlab_sec and the main gitlab schema).

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How to set up and validate locally

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Related to #512592 (closed)