[Task] Rework browser-propagation

[EddeCCC]

Is your feature request related to a problem? Please describe. Currently, it is possible to exchange tags via browser-propagation with remote services. However, this requires additional API calls to the agent (GET and PUT). It would be more convenient to allow such data exchange within the ordinary propagation, which uses data from the instrumented methods.

Describe the solution you'd like It should be possible to define data-keys, which should be propagated to remote services (UP and DOWN). Maybe, this is already possible with the GLOBAL propagation. The new solution should not replace the the browser-propagation, but exist in parallel for the first time.

Additional context The agent should not expose any APIs. It should only request data as a client.