rntbd: capture request/response length in the request diagnostics

[moderakh]

This PR adds RNTBD request length and response length to the request diagnostics. This helps in troubleshooting cases where the latency is high (e.g., rntbd transit time is high).

The following section added to request diagnostics:

"rntbdRequestLengthInBytes": 415,
"rntbdResponseLengthInBytes": 768,
"requestPayloadLengthInBytes": 0,
"responsePayloadLengthInBytes": 303

rntbdRequestLengthInBytes represents the full rntbd request length including headers and payload
requestPayloadLengthInBytes represents the request payload size only.
similarly rntbdResponseLengthInBytes and responsePayloadLengthInBytes are defined.

full diagnostics:

{
	"userAgent": "azsdk-java-cosmos/4.6.0-beta.1 MacOSX/10.15.6 JRE/11.0.6",
	"requestLatencyInMs": 2,
	"requestStartTimeUTC": "2020-09-24T06:38:01.049335Z",
	"requestEndTimeUTC": "2020-09-24T06:38:01.052043Z",
	"connectionMode": "DIRECT",
	"responseStatisticsList": [{
		"storeResult": {
			"storePhysicalAddress": "rntbd://10.37.129.3:10253/apps/DocDbApp/services/DocDbServer10/partitions/a4cb4956-38c8-11e6-8106-8cdcd42c33be/replicas/1p/",
			"lsn": 1720,
			"globalCommittedLsn": -1,
			"partitionKeyRangeId": "0",
			"isValid": true,
			"statusCode": 200,
			"subStatusCode": 0,
			"isGone": false,
			"isNotFound": false,
			"isInvalidPartition": false,
			"requestCharge": 1.0,
			"itemLSN": 1720,
			"sessionToken": "-1#1720",
			"exception": null,
			"transportRequestTimeline": [{
				"eventName": "created",
				"durationInMicroSec": "19",
				"startTime": "2020-09-24T06:38:01.050130Z"
			}, {
				"eventName": "queued",
				"durationInMicroSec": "193",
				"startTime": "2020-09-24T06:38:01.050149Z"
			}, {
				"eventName": "pipelined",
				"durationInMicroSec": "470",
				"startTime": "2020-09-24T06:38:01.050342Z"
			}, {
				"eventName": "transitTime",
				"durationInMicroSec": "1027",
				"startTime": "2020-09-24T06:38:01.050812Z"
			}, {
				"eventName": "received",
				"durationInMicroSec": "135",
				"startTime": "2020-09-24T06:38:01.051839Z"
			}, {
				"eventName": "completed",
				"durationInMicroSec": "1",
				"startTime": "2020-09-24T06:38:01.051974Z"
			}],
			"rntbdRequestLengthInBytes": 414,
			"rntbdResponseLengthInBytes": 769,
			"requestPayloadLengthInBytes": 0,
			"responsePayloadLengthInBytes": 303
		},
		"requestResponseTimeUTC": "2020-09-24T06:38:01.052043Z",
		"requestResourceType": "Document",
		"requestOperationType": "Read"
	}],
	"supplementalResponseStatisticsList": [],
	"addressResolutionStatistics": {},
	"regionsContacted": ["https://10.37.129.3:8081/"],
	"retryContext": {
		"retryCount": 0,
		"statusAndSubStatusCodes": null,
		"retryLatency": 0
	},
	"metadataDiagnosticsContext": {
		"metadataDiagnosticList": null
	},
	"serializationDiagnosticsContext": {
		"serializationDiagnosticsList": null
	},
	"gatewayStatistics": null,
	"systemInformation": {
		"usedMemory": "77966 KB",
		"availableMemory": "16699250 KB",
		"systemCpuLoad": "empty"
	}
}

[kushagraThapar]

LGTM

[moderakh]

/azp run java - cosmos - tests

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