Allow minion floating IPs to be optional

[jamiehannaford]

What this PR does / why we need it:

Makes the generation of floating IPs for worker nodes optional, based on an env var. To quote the original issue:

Currently, the OpenStack installation method assigns a floating IP to every single worker node. While this is fine for smaller clusters with a good sized IP pool, it can cause issues in environments with high node counts or less IPs available.

Which issue this PR fixes:

#40737

Special notes for your reviewer:

I used the conditions section of the Heat spec: https://docs.openstack.org/developer/heat/template_guide/hot_spec.html#conditions-section

Release note:

OpenStack clusters can now specify whether worker nodes are assigned a floating IP

[k8s-ci-robot]

Hi @jamiehannaford. 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 @k8s-bot 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.

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[k8s-reviewable]

This change is 

[eparis]

@k8s-bot test this
@k8s-sig-openstack-pr-reviews I know hot to spell heat, and not much more. Anyone on the OpenStack sig willing to take this review?

[hogepodge]

Nothing jumps out as incorrect in this template. It addresses a second major mode of network connectivity in OpenStack deployments.

[jamiehannaford]

@eparis @hogepodge Do I need to incorporate anything else or is this approved?

[eparis]

/lgtm

[k8s-github-robot]

[APPROVALNOTIFIER] This PR is APPROVED

The following people have approved this PR: eparis, jamiehannaford

Needs approval from an approver in each of these OWNERS Files:

• cluster/OWNERS [eparis]

We suggest the following people:
cc @roberthbailey
You can indicate your approval by writing /approve in a comment
You can cancel your approval by writing /approve cancel in a comment

[k8s-github-robot]

Automatic merge from submit-queue (batch tested with PRs 41297, 42638, 42666, 43039, 42567)