refactor(telemetry): use the current name for the OTLP gRPC exporter

The pinned collector warns on every start that "otlp" is a deprecated alias
for "otlp_grpc". Rename the trace exporter to otlp_grpc/tempo.

Only the exporter is affected. The otlp RECEIVER keeps its name: it serves
both gRPC and HTTP under one component and is not deprecated, verified by
renaming the exporter alone and seeing the warning stop.

This belongs on this branch because it introduces the exporter, and it is the
last of four deprecated aliases in the collector config; the other three are
owned by later branches in the chain.

OpenTelemetryPlan/05-configuration-reference.md

@@ -101,7 +101,7 @@ The authoritative collector config lives in the repo at `docker/telemetry/otel-c
 
 ### 5.5.1 Development Configuration
 
-The development collector enables an OTLP receiver on both gRPC (`0.0.0.0:4317`) and HTTP (`0.0.0.0:4318`), a single `batch` processor (1s timeout, batch size 100), and two exporters: a `logging` exporter for console debugging and `otlp/tempo` (insecure) for trace visualization. The single `traces` pipeline wires receiver → batch → both exporters.
+The development collector enables an OTLP receiver on both gRPC (`0.0.0.0:4317`) and HTTP (`0.0.0.0:4318`), a single `batch` processor (1s timeout, batch size 100), and two exporters: a `logging` exporter for console debugging and `otlp_grpc/tempo` (insecure) for trace visualization. The single `traces` pipeline wires receiver → batch → both exporters.
 
 ### 5.5.2 Production Configuration
 

docker/telemetry/otel-collector-config.yaml

@@ -52,7 +52,7 @@ processors:
 exporters:
   debug:
     verbosity: detailed
-  otlp/tempo:
+  otlp_grpc/tempo:
     endpoint: tempo:4317
     tls:
       insecure: true
@@ -67,4 +67,4 @@ service:
     traces:
       receivers: [otlp]
       processors: [resource/tier, resource/stripsdk, batch]
-      exporters: [debug, otlp/tempo]
+      exporters: [debug, otlp_grpc/tempo]