Add support for Instance Alias IP Ranges

[jwmay2012]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Allows instances to be created with a Secondary Alias IP/CIDR Range configured.
https://cloud.google.com/vpc/docs/alias-ip

This enables things like Cilium to use Google Cloud's networks for Native Routing.
By giving each pod/service an IP from the Alias IP Range.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Add support for Instance Alias IP Ranges. `GCPMachine.Spec.AliasIPRanges` This allows for [Native Routing](https://docs.cilium.io/en/stable/network/concepts/routing/#google-cloud).

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @jwmay2012. Thanks for your PR.

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[damdo]

/ok-to-test

[jwmay2012]

Rebased.
We're running this code and it's helping us enable Native Routing for our Pods in GCP.
Let me know if there's anything else to be done before merge :)

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[jwmay2012]

Having the ability to utilize Native Networking in GCP for pods and services from CAPI && CAPG is pretty neat and enabled by being able to configure these Alias IP Ranges.
We're still using this for our clusters but would love to get it upstreamed and stop using our custom build :)
A pretty standard GCPMachine spec addition and conversion to the existing GCP SDK structs.

Is there something I could do to help move this ticket forward? Thanks :)

[damdo]

Would you please explicitly mark these fields as required?
Do we need any other form of openAPI schema validation for these two fields?

Maybe something similar to this for example? (not verified) https://github.com/openshift/api/blob/9e59a77ed2e001a28bf82cc1084699a4989bba23/operator/v1/types_ingress.go#L452-L459

[damdo]

I think this would be a good addition.
Any thoughts @cpanato @salasberryfin @richardcase ?