Add no_proxy env in logstash systemd service

[RuTHlessBEat200]

Currently, only an HTTP(S) proxy can be added as an environment variable. It would also be useful to be able to set a NO_PROXY variable for domains that should not go through the proxy. We currently have the problem that plugins which are not from Elastic (in our case Loki from Grafana) want to send all traffic through the proxy, which results in a high load and a detour in the network.