docs: add ACK RRSA supported AliDNS webhook

[crazygit]

Description

This PR adds a link to a community-maintained Alibaba Cloud DNS (AliDNS) webhook solver to the documentation.

Details

I have developed a custom webhook for AliDNS based on the cert-manager/webhook-example.
It allows users to solve ACME DNS01 challenges using Alibaba Cloud DNS with ACK RRSA feature.

• Repository: crazygit/cert-manager-alidns-webhook
• Testing: I have implemented both unit tests and integration tests to verify the solver functionality. All tests passed successfully. I also have verified the webhook functionality in ACK cluster.

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[crazygit]

@hawksight @erikgb Could you please review this PR? If it looks good, a /lgtm would be appreciated. Thanks!

[erikgb]

This looks a bit odd. I am no expert on AliDNS, but why didn't you contribute "ACK RRSA" to the AliDNS webhook linked in the line above?

[crazygit]

@erikgb Thanks for the question — I agree it’s important to avoid unnecessary duplication.

• What’s different here: this repo is designed around ACK RRSA / OIDC and the Alibaba Cloud SDK default credential chain, so authentication happens on the webhook side without putting AK/SK into Issuer secrets. The existing AliDNS webhook is AK/SK‑based, configured via Issuer secrets, so the auth model is quite different.

• Why I didn’t submit to the other repo: adding RRSA support there would likely be more than a small patch — it would involve changes to the auth flow, config schema, and docs, and I wanted to avoid disrupting existing AK/SK users. I also wanted to keep the RRSA‑first approach focused and clear, since it targets newer cert-manager versions and the ACK RRSA identity scenario specifically.

Thanks for considering this and for the review.