Support portNumber and bearer_token_file for etcd integration

[fplantinga-guida]

In our Kubernetes setup (deployed with Rancher) we use a service and servicemonitor from the kube-prometheus-stack to monitor etcd. We tried to convert this to the alloy integration but we have hit the following issues:

• Rancher etcd pod manifest doesn't specify a portName because it is running with hostNetwork. Unfortunately It is not possible to specify a portNumber in the etcd module.
• If the above is possible we still need the prometheus.scrape to have the bearer_token_file argument as the metrics can't be scraped without authentication.

Is this something you are going te support?