Send host.id received from profiler via IntakeV2 metadata

[JonasKunz]

The universal profiling feature requires the host.id to be set for providing accurate CO2 and cost estimates.
For this reason, the profiling host agent sends the host.id via the domain socket to the apm-agent.

In addition elastic/apm-data#246 added support for receiving the host.id via IntakeV2 metadata.
Therefore we should take the host.id received from the profiler and send it as metadata.

Note that the profiler might initiate the correlation a while after the agent has already started. Therefore we will need to be able update the cached metadata to include the host.id.