Add vagrant boxes caching to CI

[VannTen]

What type of PR is this?
/kind feature

What this PR does / why we need it:
We're hitting 429 responses when running lots of jobs, presumably
because we are downloading lots of boxes again and again.
This should cache them instead.

Does this PR introduce a user-facing change?:

NONE

/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: VannTen

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [VannTen]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

@VannTen: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubespray-yamllint	2803946	link	true	/test pull-kubespray-yamllint

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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. I understand the commands that are listed here.

[VannTen]

This is apparently not enough because the CI runners can't extract the cache because they don't have gitlab-runner :
https://gitlab.com/kargo-ci/kubernetes-sigs-kubespray/-/jobs/7698277164#L124

[VannTen]

@ant31 if you have an idea

[ant31]

It's 429 from which service ?

[VannTen]

https://gitlab.com/kargo-ci/kubernetes-sigs-kubespray/-/jobs/7698277164#L524 I think it's app.vagrantup.com for the vagrant boxes used by molecule.