[release-1.6] 🐛 Restore v1alpha3/v1alpha4 conversion to fix SSA issue & add e2e test coverage

[sbueringer]

What this PR does / why we need it:
Manual cherry-pick of #10147

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 #

[sbueringer]

/test pull-cluster-api-e2e-main-release-1-6

[k8s-ci-robot]

@sbueringer: The specified target(s) for /test were not found.
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[sbueringer]

/test pull-cluster-api-e2e-release-1-6

[sbueringer]

/test pull-cluster-api-e2e-release-1-6

[g-gaston]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: b49f736855ddae21d0de0b19b9481cbdd1bee5ac

[sbueringer]

/test pull-cluster-api-e2e-release-1-6

Had a version mismatch v1.5.5 != v1.5.0. I think it worked locally because I still had v1.5.5 in _artifacts

[fabriziopandini]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini

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[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 211d90ccb0bfb8c2a75d00e7394cd0187576b402