Make NAT Gateway reconcile/delete async

[Jont828]

What type of PR is this?

/kind feature
What this PR does / why we need it: Implementation of an async service for NAT gateways as a follow up for #1610 and #1541.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #1714

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Make NAT gateway reconcile/delete async

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Jonathan Tong (e8a206b, 78d1c1d)

[k8s-ci-robot]

Hi @Jont828. Thanks for your PR.

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[Jont828]

/assign mboersma
/assign shysank
/assign CecileRobertMichon

I'd appreciate feedback on the reconcile/delete logic. I'm curious about if we need to set the subnets at the end of a Reconcile() loop since I don't believe removing it would change any behavior. And btw I'm holding off on refactoring the tests until the reconcile/delete functions are at a good spot.

[CecileRobertMichon]

Could you please open an issue for this? We're treating NAT gateways as if they only had 1 IP in the API but really they can have a list of associated public IPs.

[CecileRobertMichon]

cc @jackfrancis

[Jont828]

I pushed the changes to implement hasPublicIP instead, which I think gets us around this issue since we search all the public IPs in a NAT gateway.

[CecileRobertMichon]

/ok-to-test

[CecileRobertMichon]

Please squash commits

[CecileRobertMichon]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CecileRobertMichon

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[CecileRobertMichon]

/lgtm cancel

[CecileRobertMichon]

/lgtm

[k8s-ci-robot]

@Jont828: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-azure-apidiff	154bf95	link	false	/test pull-cluster-api-provider-azure-apidiff

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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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. I understand the commands that are listed here.