add compressed_payload field to both RpcRequest and RpcResponse

[xianshijing-lk]

So that we don't need to use base64 to encode the string, which adds 33% of overhead

[changeset-bot]

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Latest commit: 840ee54

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[boks1971]

Is an alternative a possible consideration? A field like

enum Encoding {
     BASE64 = 0;   --> to ensure default remains the same
     COMPRESSION_TYPE_1 = 1; 
     COMPRESSION_TYPE_2 = 2;
}

This allows an extensible format and we can have any encoding.