Fix the destruction order of handle & destroy_flags

[filimonov]

The MemorySanitizer detected a use-of-uninitialized-value issue caused by the destruction order in KafkaHandleBase. Specifically, the deleter of the Kafka handle accessed destroy_flags_ after it had been destroyed because destroy_flags_ was declared after handle_.

This commit reorders the member declarations so that destroy_flags_ is declared before handle_. The constructor's initializer list is also updated accordingly to match the new declaration order.

[filimonov]

example report from the memory sanitizer:

==28==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x5555952c97dc in cppkafka::KafkaHandleBase::HandleDeleter::operator()(rd_kafka_s*) build_docker/./build_docker/./contrib/cppkafka/src/kafka_handle_base.cpp:303:5
    #1 0x5555952c51dc in std::__1::unique_ptr<rd_kafka_s, cppkafka::KafkaHandleBase::HandleDeleter>::reset[abi:ne190107](rd_kafka_s*) build_docker/./contrib/llvm-project/libcxx/include/__memory/unique_ptr.h:292:7
    #2 0x5555952c51dc in std::__1::unique_ptr<rd_kafka_s, cppkafka::KafkaHandleBase::HandleDeleter>::~unique_ptr[abi:ne190107]() build_docker/./contrib/llvm-project/libcxx/include/__memory/unique_ptr.h:261:71
    #3 0x5555952c51dc in cppkafka::KafkaHandleBase::~KafkaHandleBase() build_docker/./contrib/cppkafka/include/cppkafka/kafka_handle_base.h:66:40
    #4 0x5555952bebac in cppkafka::Consumer::~Consumer() build_docker/./build_docker/./contrib/cppkafka/src/consumer.cpp:99:1

  Member fields were destroyed
    #0 0x55555dec328d in __sanitizer_dtor_callback_fields (/usr/bin/clickhouse+0x896f28d) (BuildId: f0dd81bc4480871c462431322414a317857334c2)
    #1 0x5555952c5182 in cppkafka::KafkaHandleBase::~KafkaHandleBase() build_docker/./contrib/cppkafka/include/cppkafka/kafka_handle_base.h:395:9
    #2 0x5555952c5182 in cppkafka::KafkaHandleBase::~KafkaHandleBase() build_docker/./contrib/cppkafka/include/cppkafka/kafka_handle_base.h:66:40
    #3 0x5555952bebac in cppkafka::Consumer::~Consumer() build_docker/./build_docker/./contrib/cppkafka/src/consumer.cpp:99:1

SUMMARY: MemorySanitizer: use-of-uninitialized-value build_docker/./build_docker/./contrib/cppkafka/src/kafka_handle_base.cpp:303:5 in cppkafka::KafkaHandleBase::HandleDeleter::operator()(rd_kafka_s*)
Exiting