Add terraform for Azure community image gallery

[mboersma]

Adds terraform needed to recreate the basic Azure community gallery resources used to host Cluster API Provider for Azure reference images.

The managed images, SIG image versions, SIG image definitions, and staging gallery are all transient and fungible resources that will be recreated if needed by the publishing pipeline, so they do not have to be handled by terraform.

See also:

• Add pipeline for Azure community gallery image publishing kubernetes-sigs/image-builder#1578
• Use community gallery for default VM images kubernetes-sigs/cluster-api-provider-azure#5167

[mboersma]

/cc @jsturtevant @nojnhuh @ritikaguptams

I'm not entirely sure what I'm doing here, so I used the aztfexport tool against the existing resource group and massaged the output into something that looks like our existing terraform structure. Please let me know what should change.

[mboersma]

/hold for reviews

[nojnhuh]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mboersma, nojnhuh

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• infra/azure/terraform/capz/OWNERS [mboersma,nojnhuh]

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[ritikaguptams]

/lgtm

[mboersma]

/hold cancel