Response Time Observability - C SDK

We need Threshold logging / tracing docs for each individual SDK. There are some links in Matt's blog post.

Take a look at https://developer.couchbase.com/documentation/server/5.5/sdk/dotnet/threshold-logging.html and note any differences; we need:

1. Any differences in Threshold Configuration Settings
2. An example along the lines of Michael's blog post.

I'll merge this into a new doc.

Also need to make sure that the examples in each SDK's docs cover the points from DOC-3102:

• document new timing info coming from server
• setting "slow operation" threshold on client
• setting "slow operation" threshold on server
• example of saving slow operations to client logs
• example of capturing client timing to get an overall timing of operation

I'm sure LCB will have some special differences, Sergey Avseyev, just ping me any concerns.