[BUG] Instrument NodeJs App in Azure App Services with serverless-init causes Cannot find module 'dd-trace/init'

[chanep]

Following the instructions for
Instrument Azure App Service with serverless-init - Linux Containers
in https://docs.datadoghq.com/serverless/guide/azure_app_service_linux_containers_serverless_init/
for an NodeJs app does not work

Agent Environment
NodeJs in Azure App Service with serverless-init - Linux Containers

Describe what happened:
When the container starts fails with
Error: Cannot find module 'dd-trace/init'

The Dockerfile in the documentation is wrong

COPY --from=datadog/serverless-init:1 /datadog-init /app/datadog-init
RUN npm install --prefix /dd_tracer/node dd-trace  --save
ENV DD_SERVICE=datadog-demo-run-nodejs
ENV DD_ENV=datadog-demo
ENV DD_VERSION=1
ENTRYPOINT ["/app/datadog-init"]
CMD ["/nodejs/bin/node", "/path/to/your/app.js"]

this
RUN npm install --prefix /dd_tracer/node dd-trace --save
does not install dd-trace in the folder /app/datadog-init expects

/app/datadog-init tries to load a module in /dd_tracer/node that actually got installed in /dd_tracer/node/node_modules