feat: get_system_identity for matching a node to its BMC (0.2.0)

Mixes in napalm-device-types 4.9's SystemIdentityMixin over the exec
path, which runs as root: the node's SMBIOS system UUID, product serial
and board serial, vendor placeholders empty. pve-dual, a Supermicro
X10DRL-i, reports the product serial 0123456789; its board serial and
UUID are what tie it to its BMC.

CHANGELOG.md

@@ -8,6 +8,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 ### Added
+- `get_system_identity()` (napalm-device-types 4.9 `SystemIdentityMixin`): the node's SMBIOS
+  system UUID, product serial and board serial over the exec path, vendor placeholders
+  empty. netOrk matches a server to its BMC on these. Requires napalm-device-types 4.9.0;
+  version 0.2.0.
 - FreeBSD and OpenBSD guests: `create_vm_from_cloud_init(guest_os=...)` with
   `GUEST_AGENTS` from napalm-device-types 3.0. A BSD guest gets OS type
   `other` and a network-config v2 snippet of its own (`cicustom network=`),