[GCS] impl RedisStoreClient for GCS Service

[micafan]

This PR is for GCS Fault Tolerance:

GCS Service use Persistent Storage to store key information. This PR implement the RedisStoreClient which use Redis as Persistent Storage.

Some complex functions are not implemented and will be completed in subsequent PRs.

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• Testing Strategy
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  • Release tests
  • This PR is not tested (please justify below)

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[mehrdadn]

Hi folks! Unfortunate news—it seems this PR broke something on Windows (which we don't have tests running for yet), and it's not clear to me what's going on. Would someone be able to help me figure out what's going on? I'm not really familiar with XADD (is it a recent Redis feature?), so it's not clear to me how to handle this. If we're now depending on Redis 5 features or if this is otherwise difficult to fix, can we revert this PR and hold off on it until we can get it working on Windows?

(cc @raulchen @micafan)

F0402 05:45:47.700804 23788 redis_context.cc:70]  Check failed: false Got an error in redis reply: ERR unknown command `XADD`, with args beginning with: `ef0a6c220100`, `*`, `signal`, `ACTOR_DIED_SIGNAL`,
*** Check failure stack trace: ***
    @   00007FF79A0A6D3D  google::LogMessage::Fail
    @   00007FF79A0A60E7  google::LogMessage::SendToLog
    @   00007FF79A0A6984  google::LogMessage::Flush
    @   00007FF79A0A67F6  google::LogMessage::~LogMessage
    @   00007FF799E0911A  ray::RayLog::~RayLog
    @   00007FF799E6FC84  ray::gcs::CallbackReply::CallbackReply
    @   00007FF799E7EFF9  std::_Ref_count_obj<ray::gcs::CallbackReply>::_Ref_count_obj<redisReply *&>
    @   00007FF799E74D02  std::make_shared<ray::gcs::CallbackReply,redisReply *&>
    @   00007FF799E71286  ray::gcs::GlobalRedisCallback
    @   00007FF79A0CD7CF  __redisRunCallback
    @   00007FF79A0CD1D4  redisProcessCallbacks
    @   00007FF79A0CD8B6  redisAsyncHandleRead
    @   00007FF79A0CF3A2  ray::gcs::RedisAsyncContext::RedisAsyncHandleRead
    @   00007FF79A58ED77  RedisAsioClient::handle_read