feat: read the virtual IPs vip-manager and keepalived declare on a host

A virtual IP sits on whichever member holds it right now; a standby's
address list shows no trace of it. What every member has is the
configuration that declares it, and reading that is the same on every
Linux host -- so VirtualIpsMixin.get_virtual_ips() lives here and a driver
only carries the command across (NetOrk/netork#829).

- vip-manager: every vip-manager.service / vip-manager@*.service unit; the
  address from a flag (1.x's -ip=${VIP_IP} resolved through the unit's
  environment), the environment, or the --config YAML (5.x).
- keepalived: the virtual_ipaddress(_excluded) entries of every
  vrrp_instance, with its interface and virtual_router_id; include is
  followed four levels deep, and a pattern that is no plain path glob is
  never handed to the root shell.

The same files hold the etcd password and auth_pass, so an awk program
filters on the host and prints allowlisted fields only. None per
mechanism is "did not look", [] a host without it. The command is about
4 kB and goes on an exec channel.

Version 4.2.0.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "napalm-device-types"
-version = "4.1.0"
+version = "4.2.0"
 description = "Abstract device-type base classes for NAPALM drivers"
 readme = "README.md"
 requires-python = ">=3.10"