[FEAT] buffer implementation

[gaurav7261]

Summary

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

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[rschu1ze]

@antaljanosbenjamin ^^

[antaljanosbenjamin]

I think @chernser is a better person to review this, as I don't have experience with this repo, only the Kafka table engine.