Allow managed images for Azure instance groups

[NickSchleicher]

Allows us to use our own managed images for virtual machine scale sets and not just ones that are published to the marketplace.

Related to
Be able to configure some more parameters for VM Scale Set such as Windows in #10412

Not sure if it's necessary we should check for a
/subscriptions/<subscription id>/resourceGroups/<resource group>/providers/<provider>/images/<image> format

[k8s-ci-robot]

Hi @NickSchleicher. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[rifelpet]

/ok-to-test

This looks good to me. For reference, cluster-api doesn't perform any input validation on the ID contents so I think its acceptable for kops not to either: https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/29ba7f37f1f1e2274bee24bc66ef9561dd158c73/api/v1alpha3/azureimage_validation.go

[NickSchleicher]

Thanks for that reference @rifelpet was curious on the protocol for things like that, will remember in the future

[rifelpet]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: NickSchleicher, rifelpet

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [rifelpet]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment