Kafka gateway: Kafka DeleteRecords — trim topic to offset via Iggy retention

[ryerraguntla]

Part of #3560.

Summary

Implement DeleteRecords (21) — trim topic/log to a specific offset, mapped to Iggy retention or explicit delete where supported.

Depends on

• Kafka gateway: Kafka DeleteTopics, DescribeConfigs, and AlterConfigs admin APIs #3546 — DeleteTopics / admin foundation

Scope

• Decode DeleteRecords request
• Map to Iggy retention trim or document limitation
• Per-partition low watermark in response
• Test: delete records before offset X; Fetch cannot read deleted range

Acceptance criteria

• Behavior documented if Iggy cannot trim arbitrarily (partial support OK with clear errors)

References

• Rollout plan: feature - Order of Implementation discussion of kafka to iggy bridge #3253 (comment)