crash at cert change

When the cert changes, HS restarts grpc server in the nuraft mesg. However, if rpc requests are active during the restart, a crash may occur. We need to ensure servers restart gracefully to prevent this.

The stack is :

(gdb) bt
#0  0x000072f0fdbb6b2c in pthread_kill () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x000072f0fdb5d27e in raise () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x000072f0fdb408ff in abort () from /lib/x86_64-linux-gnu/libc.so.6
#3  0x00006434a43b3db8 in grpc_core::Crash (message="ASSERTION FAILED: grpc_cq_begin_op(cq_, notify_tag)", location=...) at /home/ubuntu/.conan2/p/b/grpc66871916605d2/b/src/src/core/lib/gprpp/crash.cc:30
#4  0x00006434a43b1fca in gpr_assertion_failed (filename=0x6434a446d9d0 "/home/ubuntu/.conan2/p/b/grpc66871916605d2/b/src/src/core/lib/surface/call.cc", line=1855, message=<optimized out>)
    at /usr/include/c++/11/string_view:137
#5  0x00006434a3cbb2f9 in grpc_core::FilterStackCall::StartBatch (this=<optimized out>, ops=<optimized out>, nops=3, notify_tag=<optimized out>, is_notify_tag_closure=<optimized out>)
    at /home/ubuntu/.conan2/p/b/grpc66871916605d2/b/src/src/core/lib/surface/call.cc:1855
#6  0x00006434a3cb1fb1 in grpc_call_start_batch (call=0x72efe801c890, ops=0x72f026feeec0, nops=3, tag=0x72effc437d30, reserved=<optimized out>)
    at /home/ubuntu/.conan2/p/b/grpc66871916605d2/b/src/src/core/lib/surface/call.cc:3539
#7  0x00006434a32ab517 in grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata, grpc::internal::CallOpSendMessage, grpc::internal::CallOpServerSendStatus, grpc::internal::CallNoOp<4>, grpc::internal::CallNoOp<5>, grpc::internal::CallNoOp<6> >::ContinueFillOpsAfterInterception (this=0x72effc437d30) at /home/ubuntu/.conan2/p/b/grpc66871916605d2/p/include/grpcpp/impl/call.h:70
#8  0x00006434a376cf79 in grpc::internal::call::PerformOps (ops=0x72effc437d30, this=0x72effc437b98) at /home/ubuntu/.conan2/p/b/grpc66871916605d2/p/include/grpcpp/impl/call.h:67
#9  grpc::ServerAsyncResponseWriter<nuraft_mesg::RaftGroupMsg>::Finish (tag=0x72effc438598, status=..., msg=..., this=0x72effc437b90)
    at /home/ubuntu/.conan2/p/b/grpc66871916605d2/p/include/grpcpp/support/async_unary_call.h:356
#10 sisl::RpcData<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg, false>::do_non_streaming_send (this=0x72effc437710) at /home/ubuntu/sisl/include/sisl/grpc/rpc_call.hpp:345
#11 0x00006434a375f855 in boost::asio::detail::binder0<nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> >::operator() (this=0x72f026fef3f0) at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/bind_handler.hpp:60
#12 boost::asio::asio_handler_invoke<boost::asio::detail::binder0<nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> > > (function=...) at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/handler_invoke_hook.hpp:88
#13 boost_asio_handler_invoke_helpers::invoke<boost::asio::detail::binder0<nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> >, nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> > (context=...,
    function=...) at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/handler_invoke_helpers.hpp:54
#14 boost::asio::detail::asio_handler_invoke<boost::asio::detail::binder0<nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> >, nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> > (
    this_handler=0x72f026fef3f0, function=...) at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/bind_handler.hpp:111
#15 boost_asio_handler_invoke_helpers::invoke<boost::asio::detail::binder0<nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> >, boost::asio::detail::binder0<nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> > > (context=..., function=...) at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/handler_invoke_helpers.hpp:54
#16 boost::asio::detail::executor_op<boost::asio::detail::binder0<nuraft_mesg::proto_service::raftStep(sisl::AsyncRpcDataPtr<nuraft_mesg::Messaging, nuraft_mesg::RaftGroupMsg, nuraft_mesg::RaftGroupMsg>&)::<lambda()> >, std::allocator<void>, boost::asio::detail::scheduler_operation>::do_complete(void *, boost::asio::detail::scheduler_operation *, const boost::system::error_code &, std::size_t) (
    owner=0x6434ee0b16d0, base=<optimized out>) at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/executor_op.hpp:71
#17 0x00006434a3763e47 in boost::asio::detail::scheduler_operation::complete (bytes_transferred=0, ec=..., owner=0x6434ee0b16d0, this=0x72efe00c4140)
    at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/scheduler_operation.hpp:40
#18 boost::asio::detail::scheduler::do_run_one (this=this@entry=0x6434ee0b16d0, lock=..., this_thread=..., ec=...)
    at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/impl/scheduler.ipp:493
#19 0x00006434a375d671 in boost::asio::detail::scheduler::run (this=0x6434ee0b16d0, ec=...) at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/impl/scheduler.ipp:210
#20 0x00006434a376456d in boost::asio::thread_pool::thread_function::operator() (this=<optimized out>) at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/impl/thread_pool.ipp:39
#21 boost::asio::detail::posix_thread::func<boost::asio::thread_pool::thread_function>::run (this=<optimized out>)
    at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/posix_thread.hpp:86
#22 0x00006434a37606f4 in boost::asio::detail::boost_asio_detail_posix_thread_function (arg=0x6434ee0b4d80)
    at /home/ubuntu/.conan2/p/b/boost772ff092bb6cd/p/include/boost/asio/detail/impl/posix_thread.ipp:74
#23 0x000072f0fdbb4aa4 in ?? () from /lib/x86_64-linux-gnu/libc.so.6

The stack reaches sisl/grpc/rpc_call.hpp through nuraft_mesg::proto_service::raftStep and ServerAsyncResponseWriter::Finish; start there and trace the certificate-triggered restart path. Reproduce the failure with active RPC requests during a certificate change and verify that the server restarts without the gRPC assertion crash.