feat(gateways): Kafka Gateway add DeleteTopics API Key that deletes the Iggy topic only - #4400

Which issue does this PR address?

Partially closes #3546 (Part 1)
Relates to #3560

Rationale

Kafka clients remove a topic with DeleteTopics (API key 20). Issue #3546 asks the gateway to delete the Iggy stream and the Iggy topic. Unmapped Kafka topics share one default stream, and a mapping override can put two Kafka topics in the same stream, so deleting that stream would remove topics the caller did not name. This change deletes only the Iggy topic the Kafka name resolves to, and leaves the stream in place even when the delete leaves it empty. DescribeConfigs and AlterConfigs are not part of this change.

What changed?

DeleteTopics was outside the scoped API set, so the gateway closed the connection. A reading of #3546 that also deletes the Iggy stream would drop other Kafka topics that still share that stream.

Versions 1 through 5 are now advertised (version 6, the topic-id shape, is not). With the bridge on, each name deletes only the mapped Iggy topic. Success is error code 0. A missing topic returns UNKNOWN_TOPIC_OR_PARTITION (3); on version 5, where error_message is encoded, that result's text is the fixed string "internal error deleting this topic". A name that is empty, has leading or trailing whitespace, is longer than 249 bytes, is "." or "..", or contains a character outside letters, digits, ".", "_", and "-" returns INVALID_TOPIC_EXCEPTION and is not sent to Iggy. The validation reason is included as error_message on version 5. Versions 1 through 4 encode the error code only.

With the bridge off, the request is still validated and every named topic is answered NOT_CONTROLLER (41), so the client does not treat the delete as done. More than 100 topic names in one request, duplicates included, returns POLICY_VIOLATION (44) for every name and deletes nothing. One missing or invalid name does not stop another name in the same request from being deleted. A name repeated in one request is removed on the first occurrence, and the later occurrence returns UNKNOWN_TOPIC_OR_PARTITION because the topic is already gone.

Local Execution

• Passed : Yes
• Pre-commit hooks ran : The following prehooks ran

Ran the following tests and are passed :

• clamp_request_timeout_rejects_a_zero_or_negative_value_up_to_the_floor
• clamp_request_timeout_caps_an_oversized_value_at_the_ceiling
• clamp_request_timeout_passes_through_a_reasonable_value_unchanged
• delete_topics_v5_huge_topic_names_count_rejected
• delete_topics_v5_desync_varint_poc_rejected
• delete_topics_v1_truncated_legacy_topic_name_rejected
• delete_topics_deletes_a_real_iggy_topic
• delete_topics_never_deletes_the_backing_stream_even_when_it_becomes_empty
• delete_topics_on_a_nonexistent_topic_returns_unknown_topic_or_partition
• delete_topics_second_occurrence_of_a_duplicate_name_is_unknown_topic_or_partition
• delete_topics_deletes_existing_topics_alongside_a_missing_one
• delete_topics_rejects_more_than_the_topic_cap
• delete_topics_over_cap_error_message_names_the_limit
• given_kafka_topics_sh_when_creating_then_deleting_a_topic_should_round_trip_through_the_bridge (kafka-topics.sh create, list, delete, list)
• supported_ranges_table_has_thirteen_entries
• golden_apiversions_v3_flexible_response_fixture
• golden_apiversions_v1_response_fixture

cargo test -p iggy-gateway-kafka --lib delete_topics::tests
cargo test -p iggy-gateway-kafka --lib delete_topics_v5_
cargo test -p iggy-gateway-kafka --lib delete_topics_v1_truncated_legacy_topic_name_rejected
cargo test -p iggy-gateway-kafka --test delete_topics_real_bridge_tests
cargo test -p iggy-gateway-kafka --test kafka_client_e2e_tests given_kafka_topics_sh_when_creating_then_deleting_a_topic_should_round_trip_through_the_bridge
cargo test -p iggy-gateway-kafka --test version_firewall_tests supported_ranges_table_has_thirteen_entries
cargo test -p iggy-gateway-kafka --test golden_wire_fixtures_tests golden_apiversions_

AI Usage

1. Which tools? Claude
2. Scope of usage? Implementation, Review
3. How did you verify the generated code works correctly? Code walkthrough and manual testing
4. Can you explain every line of the code if asked? Yes