Support correlation-context in absence of Request-Id or traceparent

[lmolkova]

Correlation-Context is used by partner teams in Microsoft to propagate arbitrary key-value pairs along with request flow and in addition to tracing identifiers (Request-Id, cV or traceparent).

When 1P app instrumented with cV attempts to work with app that is instrumented with ApplicationInsights, AppInsights ignores Correlation-Context.
It happens because Correlation-Context according to spec is an extension on top of Request-Id (or traceparent) and is not read when Request-Id is not present.

We should read Correlation-Context regardless of Request-Id (traceprent) presence.