Refactor cluster manager on client

[lzxddz]

Use these data structures to store the cluster info at DataStoreServiceClient :

 struct DssNode
    {
        std::string host_name_;
        uint16_t port_;
        brpc::Channel channel_;

        // expired_ts_ is the timestamp when the node is expired.
        // If expired_ts_ is 0, the node is not expired.
        // If expired_ts_ is not 0, the node is expired and the value is the
        // timestamp when the node is expired.
        std::atomic<uint64_t> expired_ts_{1U};
    };
    // Cached nodes info of data store service.
    std::vector<DssNode> dss_nodes_{1024};
    // Now only support one shard. dss_shards_ caches the index in dss_nodes_ of
    // shard owner.
    std::vector<std::atomic<uint32_t>> dss_shards_{1, UINT32_MAX};
    const uint64_t NodeExpiredTime = 10 * 1000 * 1000;  // 10s

dss_nodes_ caches node info that used by dss_shards_.

When update the owner of data shard or update the channel of node, we firstly update the expired_ts_ of old node.
Then, find a free node index in dss_nodes_ (the expiration time exceeds 10 seconds or expired_ts_ is 1 ).
After updated the info at free node index, change the value of shard in dss_shards_.

To avoid using mutex lock, we must promise the dss_nodes_ should not be resized. If we can not find a free node index, we should wait and retry.

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✨ Finishing touches

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch refactor-client-config

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[githubzilla]

LGTM