Adapt C++ docs to synced env var concept as used by Python SDK

[BjoernAtBosch]

Describe your changes

Python SDK uses the SDV_[service-name]_ADDRESS for telling the address of the respective service to the application if using the native middleware. This shall be used for C++ also.

Issue ticket number and link

Required by https://github.com/eclipse-velocitas/vehicle-app-cpp-sdk/issues/59

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [ ] If it is a core feature, I have added thorough tests.
• [ ] Do we need to implement analytics?
• [ ] Will this be part of a product update? If yes, please write one phrase about this update.