Support multiple device types

[amylily1011]

From: https://bugs.launchpad.net/maas/+bug/1881664

LXD can host both containers and virtual machines, unfortunately MAAS makes the assumption that any device attached to a machine must be a container.

This is reflected in the UI by showing them all under a "Containers" heading.

It feels like we may want to move away from using "containers" in the UI at all, using a more generic term like "instances" would solve the problem even without adding an extra type field.

If a type field is added, LXD could then properly indicate whether a particular instance is a container or a VM which could then be reflected in the web UI too.

[amylily1011]

This one looks like just changing the column name would fix the confusion.