feat!: report the subscription as a license, not a warning (0.4.0)

get_device_warnings is gone; netOrk names the warnings from facts
(netOrk #1111). lldpd and the pending updates were already facts
(get_packages, get_available_updates). The subscription is now
get_licenses() from napalm-device-types 4.14's LicenseMixin: one
pve-subscription entry, the API status mapped to a LicenseStatus.

The old check compared against "NotFound" while the API answers
"notfound" (seen on all four nodes), so it never fired; the mapping is
case-insensitive.

napalm_proxmox/driver.py

@@ -40,6 +40,7 @@ from napalm_device_types import (
     HostStatusMixin,
     HypervisorDriver,
     KernelFactsMixin,
+    LicenseMixin,
     ListeningSocketsMixin,
     PortSpec,
     SnmpAgentMixin,
@@ -92,6 +93,7 @@ class ProxmoxDriver(
     SystemIdentityMixin,
     SystemdServicesMixin,
     HostStatusMixin,
+    LicenseMixin,
     SnmpAgentMixin,
     EnsurePackageMixin,
     HypervisorDriver,