feat: get_service_packages, which packages a systemd service is (NetOrk/netork#1236)

Mixes in napalm-device-types' ServicePackagesMixin. The transport runs the
shared read-only command on an exec channel under sh, without sudo: it is
about 1 kB, past what the PTY takes reliably, and written for sh whatever
the login shell. Requires napalm-device-types 4.20.0; version 0.12.0.

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- `get_service_packages()` (napalm-device-types' `ServicePackagesMixin`, NetOrk/netork#1236): which installed packages each systemd service is made of — the one shipping its unit file and the one shipping its `ExecStart` binary. Read-only, on an exec channel under `sh`, without sudo. Requires napalm-device-types 4.20.0; version 0.12.0.
+
 ### Security
 - The SSH host key is verified (NetOrk/netork#1167). `open()` hands netmiko the key the caller expects for the port in `optional_args["ssh_host_keys"]` (as a `known_hosts` file that exists only while it connects, with `ssh_strict`), so any other key is refused before the login (`SshHostKeyMismatch`); without one netmiko accepts the first key. Every key seen goes to `optional_args["ssh_host_key_observer"]`. OpenMediaVault and QNAP get this through `LinuxDriver.open()`. Requires napalm-device-types 4.19.0; version 0.11.0.