Trace Compass Server connection fails in Docker-based deployment

### Bug Description:

We get an error when opening a trace in the docker-based deployment of CDT.cloud blueprint.

Feedback from Bernd:

> The trace server was started by the theia-trace-extension, however it fails querying the server for trace data. The error message is not conclusive; however, my suspicion is that it's because the theia-trace-extension is using "localhost" by default to do the TSP REST API calls. The docker container where the trace server is running, is not "localhost". It is possible to set an environment variable to configure the url for the REST API calls. The environment variable is called "TRACE_SERVER_URL" and needs to be set before the Theia application is started. See https://github.com/eclipse-cdt-cloud/theia-trace-extension#change-the-trace-server-url for more details.
>
> By the way, there was a similar issue when supporting GitPod and we made it work by setting this env variable as shown in the https://github.com/eclipse-cdt-cloud/theia-trace-extension/blob/a11489f71e64946951587f1309bd54d974bdedd7/.gitpod.yml#L24.

If you have any questions, please let me know.