Document GCS bucket retention policy impact on ClickHouse storage

Problem

The current GCS documentation (content/en/altinity-kb-integrations/altinity-kb-google-s3-gcs.md) only covers basic setup (HMAC keys, endpoint configuration) but doesn't mention an important operational caveat.

Missing Information

When a GCS bucket has a retention policy enabled, objects cannot be deleted until the retention period expires. This causes issues with ClickHouse because it regularly deletes data during:

• Part merges - old parts are removed after merge
• Mutations - replaced data is deleted
• TTL expiration - expired data is purged

If the bucket retention policy prevents deletion, old data accumulates and storage grows exponentially, leading to unexpected costs and potential operational issues.

Suggested Addition

Add a warning/note to the GCS documentation explaining:

1. Bucket retention policies prevent ClickHouse from deleting obsolete data
2. This causes continuous storage growth
3. Recommendation to disable retention policy or use a bucket without one for ClickHouse storage

If this seems like a good enhancement, I'd be happy to take this up and submit a PR.

Lies content/en/altinity-kb-integrations/altinity-kb-google-s3-gcs.md und überprüfe die vorhandenen Anleitungen zur GCS-Einrichtung. Füge eine Warnung hinzu, die erklärt, wie Aufbewahrungsrichtlinien das Löschen durch ClickHouse während Merges, Mutationen und des Ablaufs von TTL verhindern, und empfehle, einen Bucket ohne Aufbewahrungsrichtlinie zu verwenden. Als erledigt gilt die Aufgabe, wenn das Risiko von Speicherwachstum und Betriebskosten klar dokumentiert ist.