Add ability to the VPA admission-controller to reload it's certificate

[Nuckal777]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds the ability for the admission-controller to reload it's certificate on changes to the certificate file. This is useful when provisioning certificates with cert-manager.

Which issue(s) this PR fixes:

Fixes #6272.

Special notes for your reviewer:

This is based on #3462. I tried to implement the feedback already given there.

Does this PR introduce a user-facing change?

Added `reload-cert` flag to the VPA admission-controller, which will reload the certificates it use, when they change.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

None.

[linux-foundation-easycla]

• ✅ login: Nuckal777 / name: Erik Schubert (7aa0075, 1a23c10, f7a26ff)
• ❌ The email address for the commit (9623817, e40e828) is not linked to the GitHub account, preventing the EasyCLA check. Consult this Help Article and GitHub Help to resolve. (To view the commit's email address, add .patch at the end of this PR page's URL.) For further assistance with EasyCLA, please submit a support request ticket.

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @Nuckal777. Thanks for your PR.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Nuckal777
Once this PR has been reviewed and has the lgtm label, please assign krzysied for approval. For more information see the Kubernetes Code Review Process.

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

Needs approval from an approver in each of these files:

• vertical-pod-autoscaler/OWNERS

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[Shubham82]

Hi @Nuckal777
you have to sign the CLA before the PR can be reviewed.
See the following document to sign the CLA: Signing Contributor License Agreements(CLA)

[Shubham82]

To check EasyCLA

/easycla

[Nuckal777]

Hey, @Shubham82 the commits I added to #3462 after rebasing are covered by the CLA. The commits from @surajnarwade were covered in #3462. I don't know if that is sufficient.

[Shubham82]

@Nuckal777, it is due to the commits you added that do not belong to this repository. (means you rebased on commits that are not merged in kubernetes/autoscaler repo)
We always work or merge PR on the latest commits of the CA repo.

I think you have to delete those commits and then add those changes in the code yourself.

[Shubham82]

see, the commits you added showed the following message:

This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.

9623817
e40e828

[Nuckal777]

Closing in favour of #6665.