[opentelemetry-cpp] Add opentracing shim feature

[diehard2]

Is your feature request related to a problem? Please describe.

It would be helpful for me if the WITH_OPENTRACING feature was able to be activated by vcpkg. Its an option in the cmake file, but can't be turned on by vcpkg

Proposed solution

Add a feature opentracing in the list of opentelemetry-cpp's feature list

Describe alternatives you've considered

none

Additional context

No response