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.

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.