don't require APIKEY

[cristifalcas]

Is your feature request related to a problem? Please describe.
In our setup, we can send the traces directly to a local endpoint, without authentication

We can't use buildevents because it fails with:

$ buildevents build $BUILD_ID $STEP_START success
Unable to create trace URL: unable to verify API key: config.APIKey and config.WriteKey are both empty; can't verify empty key

Describe the solution you'd like

Make it possible to run buildevents without setting up an APIKEY.

Describe alternatives you've considered

Additional context