Add connection stats to Cosmos Diagnostics

[moderakh]

• Add number of RNTBD connections to the targeted replica to Cosmos Diagnostics
• Add total number of RNTBD connections in the RNTBD Connection Pool to Cosmos Diagnostics.

[ghost]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @wmengmsft, @MehaKaushik, @shurd, @anfeldma-ms

[kushagraThapar]

We have captured this information as part of the below PR:

"serviceEndpointStatistics": {
				"availableChannels": 1,
				"acquiredChannels": 0,
				"executorTaskQueueSize": 0,
				"inflightRequests": 1,
				"lastSuccessfulRequestTime": "2020-09-25T17:13:28.216Z",
				"lastRequestTime": "2020-09-25T17:13:28.215Z",
				"createdTime": "2020-09-25T17:13:26.312417Z",
				"isClosed": false

#15564

Closing this issue, @moderakh - please create a new issue for total number of RNTBD connection stats.