Background migration to fix incorrect `has_issues` columns on `vulnerability_reads`

Why are we doing this work

In #386434 (closed) we fixed a bug where the has_issues column on the vulnerability_reads table could be set incorrectly when the record was created. We need to write a background migration in order to fix the existing records.

Relevant links

Non-functional requirements

• Documentation:
• Feature flag:
• Performance:
• Testing:

Implementation plan

Write a background migration that:

1. Iterates through all vulnerability_reads records where has_issues = false
2. Check if there are any vulnerability links associated with the vulnerability. If so, update has_issues to true

Verification steps