Finalize UUID backfilling before performing cleanup

What does this MR do and why?

This MR injects a migration to finalize UUID backfilling before performing cleanup when changing the type of vulnerability_occurrences.uuid column.

We have grounds to assume it might cause data-loss.

The fix was already merged to master in Finalize UUID backfilling before column type mi... (!142537 - merged)

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).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:package-and-test-ee job has either succeeded or been approved by a Software Engineer in Test.

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