create systemd unit example (#59)

examples/systemd/netobserv-ebpf-agent

+# default settings for netobserv-ebpf-agent
+# used by systemd unit
+# /etc/default/netobserv-ebpf-agent
+
+DIRECTION=both
+FLOWS_TARGET_HOST=127.0.0.1
+FLOWS_TARGET_PORT=9999

examples/systemd/netobserv-ebpf-agent.service

+[Unit]
+Description=Netobserv eBPF Agent
+After=network.target
+
+[Service]
+EnvironmentFile=-/etc/default/netobserv-ebpf-agent
+ExecStart=/opt/netobserv-ebpf-agent/bin/netobserv-ebpf-agent
+Restart=on-failure
+Type=exec
+
+[Install]
+WantedBy=multi-user.target