Enhance docker network ipaddresspool

[eguzki]

What

metallb is configured with the network address, or subnet, of the docker network defined by kind.

docker network inspect kind looks like

[
    {
        "Name": "kind",
        "Id": "c9a255dd3206276365f3f00c6d87d921f9eb43d6e9fa8193180615c4b48a4b9f",
        "Created": "2024-02-08T19:18:10.314623672+01:00",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": true,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.18.0.0/16",
                    "Gateway": "172.18.0.1"
                },
                {
                    "Subnet": "fc00:f853:ccd:e793::/64",
                    "Gateway": "fc00:f853:ccd:e793::1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {
            "com.docker.network.bridge.enable_ip_masquerade": "true",
            "com.docker.network.driver.mtu": "1500"
        },
        "Labels": {}
    }
]

Currently, the script utils/docker-network-ipaddresspool.sh was parsing only the first item of the IPAM.Config list. When IPv6 is also there, the order of the items is not assured. So it can also be

"IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "fc00:f853:ccd:e793::/64"
                },
                {
                    "Subnet": "172.18.0.0/16",
                    "Gateway": "172.18.0.1"
                }
            ]
        },

This PR enhances the script to read only IPv4 subnets.

[codecov]

Codecov Report

Merging #418 (8d973b9) into main (133645e) will decrease coverage by 0.67%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
- Coverage   66.41%   65.75%   -0.67%     
==========================================
  Files          38       38              
  Lines        3901     3901              
==========================================
- Hits         2591     2565      -26     
- Misses       1125     1146      +21     
- Partials      185      190       +5     

Flag	Coverage Δ
integration	70.40% <ø> (-1.29%)	⬇️
unit	60.69% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
api/v1beta1 (u)	∅ <ø> (∅)
pkg/common (u)	78.59% <ø> (ø)
pkg/istio (u)	37.11% <ø> (ø)
pkg/log (u)	31.81% <ø> (ø)
pkg/reconcilers (u)	33.44% <ø> (ø)
pkg/rlptools (u)	56.46% <ø> (ø)
controllers (i)	70.40% <ø> (-1.29%)	⬇️

see 5 files with indirect coverage changes

[didierofrivia]

🍪

[eguzki]

@mikenairn ready to review. Can you check it works for you as well? 🙏

[mikenairn]

Tried locally, all seems to be working as expected 👍