Recalculate UUIDs for Vulnerabilities::Findings using UUIDv5

Summary

During discussion on #205489 (closed) it was mentioned we could reuse uuid column present on Vulnerabilities::Finding model to store UUIDv5 which would be stable enough for us to use when matching Vulnerabilities::Feedback with Vulnerabilities::Finding models.

Implementation plan

• backend Create GenerateFindingUUIDService which takes https://github.com/rails/rails/issues/37681 into consideration (see #212322 (comment 418715710) for more context)
• backend Change the StoreReport service to save findings with their UUID V5 values. Calculate them using report_type + <fingerprint of the primary_identifier> + <fingerprint of the location> + project_id
• database Remove the default value from UUID column.
• backend Adjust Security::StoreReportService to look up findings using UUIDv5 (#292236 (closed))
• database Remove duplicate rows from vulnerability_occurrences table (#292239 (closed))
• database Implement a migration to update the existing data (!47529 (merged))