Update Telemetry client with data outlined in spec

[neha-bhargava]

Fixes #3596, fixes #4119.

Changes proposed in this request

• Add a placeholder for datapoints in TokenCacheNotificationArgs. These values will be populated when cache access is done in Microsoft.Identity.Web.
• Log the data points to telemetry pipeline.

Testing

Performance impact

Documentation

• All relevant documentation is updated.

[bgavrilMS]

Naming is only blocking change, code looks ok otherwise with minor changes suggested.

[neha-bhargava]

Removed the CacheUsed variable as this can be inferred as:

if (L2Latency > 0) 
    CacheUsed = L2
else 
    CacheUsed = L1

[trwalke]

cc @neha-bhargava for one final look

[bgavrilMS]

Approved with comments.

@neha-bhargava - can you please also show Travis how you tested this E2E so that we can see some values in Kusto ? Some manual validation would be great.

[bgavrilMS]

@trwalke - please create a work item on ID.Web to track the work in the cache project.