feat: get_service_packages, which packages a node's systemd unit is (NetOrk/netork#1236)

Mixes in napalm-device-types' ServicePackagesMixin; the transport is the
node's exec path, as for the kernel facts. Read-only. Requires
napalm-device-types 4.20.0; version 0.6.0.

napalm_proxmox/driver.py

@@ -43,6 +43,7 @@ from napalm_device_types import (
     LicenseMixin,
     ListeningSocketsMixin,
     PortSpec,
+    ServicePackagesMixin,
     SnmpAgentMixin,
     SystemIdentityMixin,
     SystemdServicesMixin,
@@ -90,6 +91,7 @@ class ProxmoxDriver(
     ProxmoxRoutingMixin,
     ProxmoxSystemMixin,
     KernelFactsMixin,
+    ServicePackagesMixin,
     ListeningSocketsMixin,
     SystemIdentityMixin,
     SystemdServicesMixin,