HOSTEDCP-1185: Add flag to create a single NAT gateway

[csrwng]

What this PR does / why we need it:
When creating multi-zone hosted clusters, the --single-nat-gateway flag allows creating a single nat gateway instead of 3 and configures all cluster traffic to flow through that gateway. This is meant to be used in development and testing so that we can avoid spending on a nat gateway for every zone of a hosted cluster.

Which issue(s) this PR fixes (optional, use fixes #<issue_number>(, fixes #<issue_number>, ...) format, where issue_number might be a GitHub issue, or a Jira story:
Fixes #HOSTEDCP-1185

Checklist

• Subject and description added to both, commit and PR.
• Relevant issues have been referenced.

[openshift-ci-robot]

@csrwng: This pull request references HOSTEDCP-1185 which is a valid jira issue.

In response to this:

What this PR does / why we need it:
When creating multi-zone hosted clusters, the --single-nat-gateway flag allows creating a single nat gateway instead of 3 and configures all cluster traffic to flow through that gateway. This is meant to be used in development and testing so that we can avoid spending on a nat gateway for every zone of a hosted cluster.

Which issue(s) this PR fixes (optional, use fixes #<issue_number>(, fixes #<issue_number>, ...) format, where issue_number might be a GitHub issue, or a Jira story:
Fixes #HOSTEDCP-1185

Checklist

• Subject and description added to both, commit and PR.
• Relevant issues have been referenced.

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[openshift-ci]

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[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

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[enxebre]

do we want to also set this in the HCs created by CI and start analize impact on AWS cost?

[csrwng]

do we want to also set this in the HCs created by CI and start analize impact on AWS cost?

Yes, that's the intent

[enxebre]

do we want to also set this in the HCs created by CI and start analize impact on AWS cost?
Yes, that's the intent

I mean it seems we are not exercising the new flag change in the cli for the tests in this PR?

/lgtm

[csrwng]

I mean it seems we are not exercising the new flag change in the cli for the tests in this PR?

Sorry, I see what you mean. I was planning to do that in a separate PR.

[openshift-ci]

@csrwng: all tests passed!

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