chore: fix setup_telemetry script (#3680)

# What does this PR do?
Added missing configuration files

## Test Plan
run ./scripts/telemetry/setup_telemetry.sh
```
OTEL_SERVICE_NAME=llama_stack OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 TELEMETRY_SINKS=otel_trace,otel_metric uv run --with llama-stack llama stack build --distro=starter --image-type=venv --run
```
Navigate to grafana localhost:3000, query metrics and traces

scripts/telemetry/prometheus.yml

@@ -0,0 +1,12 @@
+global:
+  scrape_interval: 15s
+  evaluation_interval: 15s
+
+scrape_configs:
+  - job_name: 'prometheus'
+    static_configs:
+      - targets: ['localhost:9090']
+
+  - job_name: 'otel-collector'
+    static_configs:
+      - targets: ['otel-collector:9464']