Avoid partition scan in Geo skip-enqueue check

What does this MR do and why?

Gitlab::Geo::LogCursor::Events::Event#skip_enqueue? added in !245426 needs to check whether a specific blob record is stored locally.

That per-event lookup was measured at ~13-15ms with a warm cache, which risks becoming a bottleneck for LogCursor's single-threaded processing loop at >100 events/second. Investigation showed the cost is almost entirely Postgres planning time: p_ci_job_artifacts (partitioned by partition_id) and uploads (partitioned by model_type) can't be pruned by a bare id lookup, so the planner builds an Append across every partition before even running the (trivially fast) per-partition scan.

This change threads the relevant partition key through the Geo event payload at creation time, where it's already in memory on the replicator. skip_enqueue? can scope its lookup by it and let Postgres prune to a single partition. Non-partitioned replicable tables are unaffected, since the extra WHERE clauses are only added when the payload carries a partition key.

Database queries

SELECT 1 AS one FROM "uploads" WHERE "uploads"."id" = 1197913122 AND "uploads"."model_type" = 'Project' LIMIT 1

Query plan: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/53884/commands/156210

SELECT 1 AS one FROM "p_ci_job_artifacts" WHERE "p_ci_job_artifacts"."id" = 18028112522 AND "p_ci_job_artifacts"."partition_id" = 100

Query plan: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/53884/commands/156213

With at most 2/3ms per query, >100events per second won't become a bottleneck for LogCursor's single-threaded processing loop, and won't cause a queue buildup. This fix is safe.

References

Fixes Geo: Logcursor enqueues blob events through ful... (#593115)

How to set up and validate locally

See !245426. The behaviour should be unchanged.

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