Write about best-practice high availability and scaling of cert-manager components

[wallrj]

Preview: https://deploy-preview-1330--cert-manager-website.netlify.app/docs/installation/best-practice/#high-availability

We've added various Helm chart values which allow users to configure cert-manager for HA and scalability, but we've never documented any recommendations explaining how these settings should be used in production.

My original / ultimate plan was to change some of the Helm chart defaults to include useful default topology constraints, as first suggested by @ThatsMrTalbot in a cert-manager dev meeting and discussed further in https://kubernetes.slack.com/archives/CDEQJ0Q8M/p1697561450000799

But first I want to document what we think the best practice settings are.

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[inteon]

/lgtm