Draft: Resolve "Transition sbom_occurrences to loose foreign keys"

What does this MR do and why?

This MR is the first step in the decomposition of the sbom_occurrences table to the new gitlab_sec schema ahead of the sec db decomposition.

The idea is to keep the change set minimal, identify cross join issues to be worked moving forward, and configure loose foreign keys for relationships that will go beyond the bounds of a single DB. (EG: sbom_occurrences -> projects)

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Related to #469536