✨ Use IPAM solution for node ips

[Mattes83]

Describe the solution you'd like:
We are using third party systems outside of kubernetes which only accept incoming traffic from certain ip ranges.
Therefore we need static node ips.

CAPV for example allows to use an IPAM provider like https://github.com/kubernetes-sigs/cluster-api-ipam-provider-in-cluster
The proposal would be to add an optional reference to an IPAddressPools in the IonosCloudMachineSpec.
The IonosCloudMachineController would create an IPAddressClaim and wait for an IPAM provider to create an IPAddress from the IPAddressClaim. When the IPAddress is created it can request the ionos api to create the server with this IP.
If there is no reference we use DHCP just like before.

type IonosCloudMachineSpec struct {
	
	// PrimaryAddressFrom is an IPAddressPools that should be assigned
	// to an IPAddressClaims.
	// +optional
	PrimaryAddressFrom *corev1.TypedLocalObjectReference `json:"primaryAddressFrom,omitempty"`
}

What do you think about the api change? If you agree I'd like to implement it.

[farodin91]

In the future, it would be good, if IONOS has it's on pool implementation to use IONOS IP Block directly.

[piepmatz]

We'll need something like this, too. I'll collect some more information and get back to you later this week.

[piepmatz]

I'm not sure about the PrimaryAddressFrom name, but we don't need to decide that now. The general idea sounds fine, so go for it! :)

I have doubts whether our general network design of having some fields related to the primary NIC only and AdditionalNetworks separated from it was a good idea. Supporting IP pools for those additional networks would be benefical, too, but that's out of scope for now and will likely be part of another API version.

Two things to keep in mind for the implementation, though:

• We want to support dual-stack from the start, IPv6 is enabled by default, also for the primary NIC. Can the IP pool feature be done in a dual-stack way with only one IPAddressPools or would we need to allow referencing two separate ones?
• This provider is aiming for feature parity with our Managed K8s offering. That involves offering private node pools, i.e. the nodes are only connected to a private network, unexposed to the Internet. However, they are behind a NAT gateway to have Internet access. In such a setup we also need IPAM to determine the node IPs in that private network. When adding that feature in this provider, the required IP pool reference(s?) will be on the IonosCloudCluster CRD. In consequence, the logic you build for this issue should be not too coupled to IonosCloudMachines, but be somewhat reusable for that future use case.