Please provide documentation on how to get the Trace button in the portal GUI to work

### Proposal

Tracing works using a managed gateway. When using a self-hosted gateway, it does not seem tracing works out of the box, as regardless of config, the message "Trace is not available because response does not contain Apim-Trace-Id header" is shown when pressing the button. Please provide documentation on how to get the Trace button in the portal GUI to work.

### Use-Case

Already works with managed gateway. Should work with self-hosted gateway. And although crafting API calls with e.g. REST Client and setting Ocp-Apim-Trace: true is possible, it is vastly more cumbersome compared to having the corresponding functionality readily available in the Trace button.

### Anything else?

_No response_