Update correlation proposal v2 in accordance to what was implemented in AI

[SergeyKanzhelev]

We are using Request-Context for both - request and response. Let's update the proposal. I'll try to send PR tomorrow.

Also mention scenarios:

Also distributed storage is not the only purpose for the Request/Response context. Beside storage identifier it can carry the:

• Version of API that “parent” request implements. It is not the correlation API version, just a parent’s request.
• Tenant that “parent” request makes work for. This tenant is not necessarily shared across all requests in the trace as backend may be tenant-neutral or batch-process data for multiple tenants
• “Parent” requests route that identifies the request and allows the grouping by it. This name is not necessarily the name you want to propagate two levels down dependencies tree and it only makes sense for immediate child for grouping
• “Parent” request device type like “mobile app v12” or “browser”

[lmolkova]

I think the best place for v2 protocol now (until and if we publishit as RFC) is one of ApplicationInsights repos. So feel free to copy it there. I also think we should somehow rebrend it - it has nothing to do with v1 and is an extension or even completely separate protocol. But still v1 is worth mentioning there.