title: How to create custom span with all details as it's created by elastic-apm-agent?
body: <p>I'm creating custom spans for outgoing requests for my java app. It works and it's great ;)
  But... when I compare my custom span on Kibana's APM board with other spans from springboot applications, which are created by elastic-apm-agent, then I can see that my spans are very low on additional details.
  I would like to have at least the URL details included in my custom span.
  The apm-agent-api doesn't allow this.</p>
  <p>Is there a way to set additional details, like url, to custom span? (I don't want to use labels for this)</p>
  <p>Thanks</p>