[Bug]: Implement httpprotobuf as open telemetry protocol.

### What happened?

While CLI implements the option to configure the protocol, the service implementation looks hard coded to GRPC. After spending many hours to get it to use httpprotobuf it looks like at a cold level its implemented to grpc.

Copilot validating:

> You’re right: service code is currently hard-coded to gRPC.
>
> Confirmed in these service paths (all set configure.Protocol = OtlpExportProtocol.Grpc; explicitly):
>
> src/Service/Program.cs (logging OTLP exporter)
> src/Service/Startup.cs (logging, metrics, tracing OTLP exporters)
> Meanwhile, config model/schema/CLI do expose exporter-protocol with grpc | httpprotobuf, but the service wiring does not read/use that value when creating exporters.
>
> So current state is:
>
> CLI/schema/config: supports httpprotobuf
> runtime exporter setup: effectively always gRPC

### Version

2.0.9

### What database are you using?

Azure SQL

### What hosting model are you using?

Local (including CLI)

### Which API approach are you accessing DAB through?

MCP

### Relevant log output

```Text

```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Beginne in src/Service/Program.cs und src/Service/Startup.cs, wo die OTLP-Exporter für Logging, Metriken und Tracing konfiguriert werden. Verfolge, wie exporter-protocol aus dem CLI-/Konfigurationsmodell geladen wird, und überprüfe dann, dass jeder Service-Exporter sowohl grpc als auch httpprotobuf unterstützt, anstatt grpc zu erzwingen; vorhandene Exporter-Tests sollten, falls vorhanden, beide Werte abdecken.

Vom Indexierungsmodell aus dem Issue-Text verfasst.