Adds logging LLM usage information using OpenTelemetry. Closes #1067

[waldekmastykarz]

Adds logging LLM usage information using OpenTelemetry. Closes #1067

To test

devproxyrc.json:

{
  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v0.27.0/rc.schema.json",
  "plugins": [
    {
      "name": "OpenAITelemetryPlugin",
      "enabled": false,
      "pluginPath": "~appFolder/plugins/dev-proxy-plugins.dll"
    }
  ],
  "urlsToWatch": [
    "http://localhost:11434/*"
  ],
  "logLevel": "information",
  "newVersionNotification": "stable",
  "showSkipMessages": true,
  "showTimestamps": true,
  "validateSchemas": true
}

Visualize using Aspire dashboard:

docker run --rm -it -p 18888:18888 -p 4317:18889 -p 4318:18890 --name aspire-dashboard mcr.microsoft.com/dotnet/aspire-dashboard:latest

Call Ollama using its OpenAI-compatible API:

curl -ikx http://127.0.0.1:8000 -X POST -H Content-Type: application/json -d '{"model":"llama3.2","messages":[{"role":"user","content":"What is the capital of France?"}],"stream":false}' http://localhost:11434/v1/chat/completions

In the Aspire dashboard, you'll see tracing and metrics (it takes a moment for metrics to show up).

To test cost estimation

devproxyrc.json

{
  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v0.27.0/rc.schema.json",
  "plugins": [
    {
      "name": "OpenAITelemetryPlugin",
      "enabled": false,
      "pluginPath": "~appFolder/plugins/dev-proxy-plugins.dll",
      "configSection": "openAITelemetryPlugin"
    }
  ],
  "urlsToWatch": [
    "http://localhost:11434/*"
  ],
  "openAITelemetryPlugin": {
    "includeCosts": true,
    "pricesFile": "llm-prices.json"
  },
  "logLevel": "information",
  "newVersionNotification": "stable",
  "showSkipMessages": true,
  "showTimestamps": true,
  "validateSchemas": true
}

llm-prices.json:

{
  "prices": {
    "llama3.2": {
      "input": 10.0,
      "output": 30.0
    }
}

Call Ollama again, check out the new span with cost information and wait for additional metrics to show up in the dashboard.