feat(binding-mqtt-kafka): deprecate Kafka-group session ownership (#1797)

[jfallows]

Summary

Deprecation announcement for Kafka consumer-group session ownership in the mqtt-kafka binding (Fixes #1797). Schema preparation plus a runtime warning, with no behavior change — the existing highlander-group ownership coordination in MqttKafkaSessionFactory is untouched.

• Add an optional store field to the mqtt-kafka binding options schema. It is parsed and validated but unused by code in this release.
• Log a one-time deprecation warning per binding instance (System.out, guarded to worker 0) when store is not configured, announcing that store will be required in an upcoming release.
• Wire store through MqttKafkaOptionsConfig, its builder, and the JSON adapter (read + write).

Acceptance criteria

• Configurations with store declared on mqtt-kafka are accepted (parsed and ignored).
• Configurations without store are accepted and log the deprecation warning once per binding instance.
• Existing MqttKafkaSessionFactory behavior is unchanged.

Notes

• The deprecation warning uses System.out.println rather than the binding event system, since it is temporary and will be removed when store-based ownership lands.
• CHANGELOG.md is auto-generated from merged PRs (github-changelog format), so it was not hand-edited — the release notes entry will be generated from this PR.
• The store schema field is currently a free string and is not yet validated against the top-level stores: section, matching the "parsed and ignored" scope for this release.

Test plan

• SchemaTest validates a new proxy.store.yaml config (10/10 passing).
• MqttKafkaOptionsConfigAdapterTest covers store read and write (6/6 passing).
• Confirm CI is green.

https://claude.ai/code/session_0186rZE8mW1U947XTN4kzZ1x

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Generated by Claude Code

[jfallows]

LGTM