Summary:
Allow containers to be launched using existing network namespaces (typically defined by the netns config)

Use Case:
Allow users to define complex network configurations in the host vyos config, and launch containers with those already set up. Also lets a container have L2 adjacency to a 'real' network (via bridges) without giving it access to all host interfaces.

Suggested CLI:

set container $container netns $netns

(conflicts with both set container $container network ... and set container $container allow-host-networks)

This also provides a workaround for T8224, by defining the netns beforehand, and launching multiple containers using it.