Feat: add certificate configuration document

[irwin9204]

What type of PR is this? /kind documentation

What this PR does / why we need it: Help users to configure certificates that use in karmada control plane

Which issue(s) this PR fixes: Part of https://github.com/karmada-io/karmada/issues/4787

Special notes for your reviewer: None

[karmada-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[karmada-bot]

Welcome @irwin9204! It looks like this is your first PR to karmada-io/website 🎉

[samzong]

@windsonsea If u have some time, please take a look. tks.