Support for network host_ipv4 label

### Feature request description

Same as https://github.com/moby/moby/issues/30053 & https://github.com/moby/libnetwork/pull/2454

It should be possible to specify a host_ipv4 & host_ipv6 because currently the default route is used.

### Suggest potential solution

Implement a way to let users specify either the interface or the IP address

### Have you considered any alternatives?

The alternatives are custom ip routes, but having it built in would be way better

### Additional context

_No response_

Start by reading Moby issue 30053 and libnetwork PR 2454, then locate netavark's current default-route handling. Determine how callers would select an interface or host_ipv4/host_ipv6, and verify that both address families no longer depend on the default route or custom routes.

Written by the indexing model from the issue text.