Backport of 'Disable async_insert in build and pipeline sync operations'

What does this MR do and why?

Backport of !219352 (merged) to 18-7-stable-ee.

Disables async_insert in ClickHouse build and pipeline sync operations to prevent data duplication in materialized views.

Problem: The ci_finished_pipelines_daily materialized view shows significant data inflation (up to 80% for some months) compared to the source ci_finished_pipelines table. Investigation revealed that HTTP read timeouts during async inserts cause the client to believe insertions failed, triggering retries that result in duplicate data.

Root cause: The async insert settings (async_insert=1, wait_for_async_insert=1) combined with ClickHouse's wait_for_async_insert_timeout=120s can exceed the Ruby HTTP client's read timeout. When this happens:

1. The HTTP client times out waiting for a response
2. The insertion may have actually succeeded in ClickHouse
3. Sidekiq retries the job, inserting the same data again
4. The source table (ReplacingMergeTree) deduplicates, but the MV (AggregatingMergeTree) accumulates duplicates

Solution: Remove async_insert settings entirely. Since we already batch data before insertion, async insert provides minimal benefit while introducing timeout-related reliability issues.

References

• Original discussion: https://gitlab.com/gitlab-org/gitlab/-/work_items/586319#note_3013011851
• Parent issue: https://gitlab.com/gitlab-org/gitlab/-/work_items/586319
• Parent MR: !219352 (merged)
• Related MR (disable retries): !219149 (merged)

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