⚠️ rename v1beta1 to v1alpha5

[apricote]

What this PR does / why we need it:

Renames the upcoming API Version from v1beta1 to v1alpha5 to avoid making commitments about the API stability. We made quite a few changes to the API and want to validate that it feels right before committing on it.

See issue #1196 for an deeper explanation.

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 #1196

Special notes for your reviewer:

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

PR on hold until we have a consensus from all maintainers for this rename.

/hold

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[seanschneeweiss]

Looks like the admissionregistration is not happy with v1alpha5.

action failed after 10 attempts: failed to create provider object admissionregistration.k8s.io/v1, Kind=MutatingWebhookConfiguration, /capo-mutating-webhook-configuration: MutatingWebhookConfiguration.admissionregistration.k8s.io "capo-mutating-webhook-configuration" is invalid: [webhooks[0].admissionReviewVersions: Invalid value: []string{"v1alpha5"}: must include at least one of v1, v1beta1, 
  occurred 

[apricote]

Yes, it looks like I overeagerly replaced a v1beta1 that referred to something other than the CAPO api group. I will push a fix tomorrow

[apricote]

/retest

Looks like a devstack failure to me

[apricote]

/retest

the e2e test succeeded recently in another pr: https://prow.k8s.io/view/gs/kubernetes-jenkins/pr-logs/pull/kubernetes-sigs_cluster-api-provider-openstack/1204/pull-cluster-api-provider-openstack-e2e-test/1514418132024823808

[apricote]

/milestone v0.6

[tobiasgiese]

/lgtm

[apricote]

/hold cancel

Just waiting for an approval now.

[jichenjc]

/approve

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[APPROVALNOTIFIER] This PR is APPROVED

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