feat: get_system_identity for matching a host to its BMC (0.7.0)

Mixes in napalm-device-types 4.9's SystemIdentityMixin: the host's
SMBIOS system UUID, product serial and board serial, read as root on an
exec channel, vendor placeholders empty. netOrk links a server's BMC to
the host on these.

CHANGELOG.md

@@ -7,6 +7,13 @@ 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 host's
+  SMBIOS system UUID, product serial and board serial, read as root on an exec channel,
+  vendor placeholders empty. netOrk matches a server to its BMC on these. Requires
+  napalm-device-types 4.9.0 or later; version 0.7.0.
+
 ### Changed
 
 - Requires napalm-device-types 4.7.1 or later; version 0.6.0.