This commit introduces gRPC-based log streaming between the VM runner (`solstice-runner`) and orchestrator. Key updates include:
- Implemented gRPC server in the orchestrator for receiving and processing runner logs.
- Added log streaming and job result reporting in the `solstice-runner` client.
- Defined `runner.proto` with messages (`LogItem`, `JobEnd`) and the `Runner` service.
- Updated orchestrator to accept gRPC settings and start the server.
- Modified cloud-init user data to include gRPC endpoint and request ID for runners.
- Enhanced message queue logic to handle job results via `publish_job_result`.
- Configured `Cross.toml` for cross-compilation of the runner.
