Backport of 'Fence the affected package lookup with a LATERAL join' to 19.5

What does this MR do and why?

Backport of Fence the affected package lookup with a LATERA... (!266238 - merged) • Orin Naaman • 19.6 to 19.5.

• Dependency Scanning jobs can time out on the each_batch probe over pm_affected_packages when Postgres plans it as a scan of the whole primary key
• The fix joins through a fenced LATERAL subquery, which keeps one index seek per component
• MalwareAffectedPackage.for_occurrences gets the same change
• The cherry-pick applied cleanly to 19-5-stable-ee

Related to https://gitlab.com/gitlab-com/request-for-help/-/work_items/5619+s

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• The MR title is descriptive (e.g. "Backport of 'title of default branch MR'"). This is important, since the title will be copied to the patch blog post.
• Required labels have been applied to this merge request
  • severity label and bug subtype labels (if applicable)
  • If this MR fixes a bug that affects customers, the customer label has been applied.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the E2E Omnibus GitLab EE pipeline (triggered by thee2e:test-on-omnibus-ee job) has succeeded. If it has failed (or shows warnings), investigate the failures. If you determine the failures are unrelated, you may proceed. If you need assistance investigating, request help in the #s_developer_experience Slack channel to confirm the failures are unrelated to the merge request.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
• Ask questions on the #releases Slack channel (internal only).
• Once the backport has been merged, the commit changes will be automatically deployed to a release environment that can be used for manual validation. See after merging runbook for details.