Change occurrences column type to join feedback table

What does this MR do and why?

This MR fixes a query performance issue by making a change to utilize an existing index.

Related to #391419 (closed) and gitlab-com/gl-infra/production#8527 (closed)

Database review

The old version of the query

SELECT
    "vulnerability_occurrences".*
FROM
    "vulnerability_occurrences"
WHERE
    "vulnerability_occurrences"."vulnerability_id" = 76821038
    AND (EXISTS (
            SELECT
                1
            FROM
                "vulnerability_feedback"
            WHERE (vulnerability_occurrences.uuid = vulnerability_feedback.finding_uuid::text)
            AND "vulnerability_feedback"."feedback_type" = 0))

Execution plan(~800ms): https://console.postgres.ai/gitlab/gitlab-production-tunnel-pg12/sessions/16341/commands/56105

The new version of the query

SELECT
    "vulnerability_occurrences".*
FROM
    "vulnerability_occurrences"
WHERE
    "vulnerability_occurrences"."vulnerability_id" = 76821038
    AND (EXISTS (
            SELECT
                1
            FROM
                "vulnerability_feedback"
            WHERE (vulnerability_occurrences.uuid::uuid = vulnerability_feedback.finding_uuid)
            AND "vulnerability_feedback"."feedback_type" = 0))

Execution plan(~9ms): https://console.postgres.ai/gitlab/gitlab-production-tunnel-pg12/sessions/16341/commands/56106

MR acceptance checklist

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