Create pipeline sync events for ClickHouse

What does this MR do and why?

This MR builds on Create p_ci_finished_pipeline_ch_sync_events table (!158060) to start creating pipeline sync events as pipelines enter an unlockable state, at which point we want to start syncing them to ClickHouse from the Ci::FinishedPipelineChSyncEvent queue. It is important to only do this when we don't expect more significant changes to a pipeline, since we treat ClickHouse as a (mostly) immutable database.

Part of #470078

MR acceptance checklist

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Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Run any pipeline in a GDK project. Once it completes, a new Ci::FinishedPipelineChSyncEvent record should be present in the database:

> Ci::FinishedPipelineChSyncEvent.pending.count
=> 1

Database query plan

Upsert

https://console.postgres.ai/gitlab/gitlab-production-ci/sessions/29664/commands/92096

INSERT INTO "p_ci_finished_pipeline_ch_sync_events" ("pipeline_id", "pipeline_finished_at", "project_namespace_id")
  VALUES (1805209, '2024-05-25 06:28:42.584935', 80)
ON CONFLICT ("pipeline_id", "partition")
  DO UPDATE SET
    "pipeline_finished_at" = excluded."pipeline_finished_at", "project_namespace_id" = excluded."project_namespace_id"
  RETURNING "pipeline_id", "partition"

 ModifyTable on public.p_ci_finished_pipeline_ch_sync_events  (cost=0.00..0.01 rows=1 width=33) (actual time=0.501..0.502 rows=1 loops=1)
   Buffers: shared hit=107 dirtied=5
   I/O Timings: read=0.000 write=0.000
   ->  Result  (cost=0.00..0.01 rows=1 width=33) (actual time=0.001..0.001 rows=1 loops=1)
         I/O Timings: read=0.000 write=0.000