Ingest identifiers to vulnerability_reads.identifiers

What does this MR do and why?

Ingests the various identifier ids of a vulnerability into the vulnerability_reads.identifier_external_ids table.

We intend to use this column for the filtering by identifier feature tracked in #432419 (closed)

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Before	After

How to set up and validate locally

1. Import the project from here into local without this MR change.
2. Run pipeline on the master branch, this should populate the identifiers and the project.vulnerability_reads.pluck(:identifier_external_ids).first(10) should have empty array values.
3. With the ingestion change from this MR, run a pipeline and project.vulnerability_reads.pluck(:identifier_external_ids).first(10) should have the identifier_ids populated.

Related to #460080 (closed)