Add a baggage example

[bryce-b]

1. Review the open-telemetry baggage API spec, and the opentelemetry-swift implementation.
2. spin up an instance of apm-integration-testing
   a. use with opbeans-dotnet, which is the only service that supports otel baggage.
   b. run example python3 ./scripts/compose.py start --with-opbeans-dotnet main
   c. kibana will be available on 127.0.0.1:5601
3. opbean-swift should automatically connect to local apm-server and opbeans service (see note below). You can make changes to these connections using agent-conf.json and apiData.json.
4. configure a baggage manager and register it OpenTelemetry.registerBaggageManager(...). Do this because default baggage manager is probably a no-op.
5. Add a new baggage attribute: request.source: opbeans-swift. This should get automatically added to all out going requests, but you can verify this by looking at opentelemetry-swift URLSession instrumentation

Note:
You'll need to expose opbeans-dotnet in docker-compose.yml (in apm-integration-testing):

...
"ports": [
  "127.0.0.1:3004:3000"
]

to

 
"ports": [
    "3004:3000"
]

then docker-compose up -d