🌱 Add optional ClusterctlVariables to QuickStartSpecInput

[neoaggelos]

What this PR does / why we need it: The e2e.QuickStartSpec is an easy spec for third party ClusterAPI providers to add e2e tests. Adding ClusterctlVariables to the input allows injecting extra variables to the template in a manner that is local to the running tests. Potential alternatives like setting environment variables or generating a separate config file per test are a lot more trouble.

When this is not specified, it is a no-op, so no breaking changes.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

/area e2e-testing

[k8s-ci-robot]

Hi @neoaggelos. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /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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[sbueringer]

/ok-to-test

[sbueringer]

/lgtm

/assign @chrischdi @fabriziopandini

/cherry-pick release-1.9

[k8s-infra-cherrypick-robot]

@sbueringer: once the present PR merges, I will cherry-pick it on top of release-1.9 in a new PR and assign it to you.

In response to this:

/lgtm

/assign @chrischdi @fabriziopandini

/cherry-pick release-1.9

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[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 4df4fd77ee0cf4fe659afe08e7b2be913c03a30c

[chrischdi]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chrischdi

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[k8s-infra-cherrypick-robot]

@sbueringer: new pull request created: #11785

In response to this:

/lgtm

/assign @chrischdi @fabriziopandini

/cherry-pick release-1.9

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.