Add tutorial and docs for grpc interface

[lukasmittag]

Describe your changes

Issue ticket number and link

Checklist before requesting a review

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

[erikbosch]

Note that this not yet in deployed to https://eclipse-velocitas.github.io/velocitas-docs/docs/concepts/development_model/vehicle_app_manifest/interfaces/grpc_interface/, as that does not happen automatically