Flatten the CDS grpc request payload

Flatten the CDS grpc request payload

Before:
{
    "vfw-modify-config-request":{
        "resolution-key":"1234567890",
        "aai-properties":{
            "service-instance.service-instance-id":"1234",
            "generic-vnf.vnf-id":"5678"
        },
        "policy-payload":{
            "data":"{\"active-streams\":\"5\"}"
        }
    }
}

After:
{
    "vfw-modify-config-request":{
        "resolution-key":"1234567890",
        "vfw-modify-config-properties":{
            "service-instance.service-instance-id":"1234",
            "generic-vnf.vnf-id":"5678",
            "data":"{\"active-streams\":\"5\"}"
        }
    }
}

Issue-ID: POLICY-2089
Signed-off-by: Rashmi Pujar <rashmi.pujar@bell.ca>
Change-Id: I139a7ca3e1e2d0cd50bbd86d0cdf499f215be74f