Add support for network forwards

[f-bn]

Hello !

In order to continue the improve the provider, having support of network forward feature could be nice.

Thanks !

[stgraber]

This should be very similar to what's been done for load-balancers: https://registry.terraform.io/providers/lxc/incus/latest/docs/resources/network_load_balancer

The applicable struct is: https://github.com/lxc/incus/blob/main/shared/api/network_forward.go

The network forward entry itself is basically:

• Listen address
• Description
• Configuration
• Ports

Then each port is:

• Description
• Protocol
• ListenPort
• TargetPort
• TargetAddress

So that should result in a incus_network_forward which looks like this:

resource "incus_network_acl" "this" {
    remote = "my-cluster"
    project = "foo"

    network = "my-network"
    listen_address = "10.0.0.1"
    description = "My network forward"

    config {
        target_address = "10.1.1.10"
    }

    port {
        description = "SSH"
        listen_port = "22"
        target_port = "2022"
        target_address = "10.1.1.1"
    }

    port {
        description = "HTTP"
        listen_port = "80"
        target_port = "8080"
        target_address = "10.1.1.2"
    }
}