Make it possible to provide a custom issuer for the certificate in the Helm chart

[bianchi2]

Description

It's a common practice to use one common issuer for all apps requiring certificates in a single cluster. This PR adds an optional certManager.existingIssuerName to values. When undefined, nothing changes and Issuer is created and referenced in the Certificate. When defined, no Issuer is created and a custom Issuer is referenced in the Certificate.

Checklist

• [ ] Added tests that cover your change (if possible)
• [ ] Added/modified documentation as required (such as the README.md, or the docs directory)
• [x] Manually tested
• [x] Made sure the title of the PR is a good description that can go into the release notes

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: bianchi2 / name: yivan-atl (887ca0230a4654746155d3e359dad0a01a21d2a1, 2f77ec179ee63cacc9b390f4e6f0e2467cb64ebd)

[k8s-ci-robot]

Hi @bianchi2. 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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[bianchi2]

Is there any chance this PR gets a review? Thanks

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bianchi2, zac-nixon

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[zac-nixon]

/lgtm /approved

Thanks for the addition! Sorry about the delay.

[bianchi2]

@zac-nixon thanks for approving it! What need to be done to be able to merge this PR? I saw a failing golint job - so I merged the latest main to my forked branch.

[k8s-ci-robot]

New changes are detected. LGTM label has been removed.

[k8s-ci-robot]

PR needs rebase.

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.