OSASINFRA-3546: openstack: document how to create a cluster

[EmilienM]

What this PR does / why we need it:

First manual to document how we can deploy a cluster with the OpenStack platform.

[openshift-ci-robot]

@EmilienM: This pull request references OSASINFRA-3546 which is a valid jira issue.

Warning: The referenced jira issue has an invalid target version for the target branch this PR targets: expected the task to target the "4.17.0" version, but no target version was set.

In response to [this](https://github.com/openshift/hypershift/pull/4414): >**What this PR does / why we need it**: > >First manual to document how we can deploy a cluster with the OpenStack platform. > Instructions for interacting with me using PR comments are available [here](https://prow.ci.openshift.org/command-help?repo=openshift%2Fhypershift). If you have questions or suggestions related to my behavior, please file an issue against the [openshift-eng/jira-lifecycle-plugin](https://github.com/openshift-eng/jira-lifecycle-plugin/issues/new) repository.

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[EmilienM]

/cc MaysaMacedo bryan-cox

[bryan-cox]

/approve

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bryan-cox, EmilienM

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/openshift/hypershift/blob/main/OWNERS)~~ [bryan-cox] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[openshift-ci[bot]]

@EmilienM: all tests passed!

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Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository. I understand the commands that are listed [here](https://go.k8s.io/bot-commands).

[MaysaMacedo]

/lgtm