Backport of docs: K8s secondary DC requirements into release/1.15.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #18280 to be assessed for backporting due to the inclusion of the label backport/1.15.

🚨

Warning automatic cherry-pick of commits failed. If the first commit failed,
you will see a blank no-op commit below. If at least one commit succeeded, you
will see the cherry-picked commits up to, not including, the commit where
the merge conflict occurred.

The person who merged in the original PR is:
@trujillo-adam
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: unable to process merge commit: "e46f988cd997572d7d6ff8d67065a9c6cc1febee", automatic backport requires rebase workflow

The below text is copied from the body of the original PR.

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Description

This PR responds to a request to highlight the Kubernetes WAN Federation requirement that when ACLs are enabled, the Kube API of the secondary datacenters must be routable from the primary datacenter.

Links

• JIRA Ticket
• Slack convo

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• 317585c - 7ca2a56 - e46f988

[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR

[hc-github-team-consul-core]

🤔 This PR has changes in the website/ directory but does not have a type/docs-cherrypick label. If the changes are for the next version, this can be ignored. If they are updates to current docs, attach the label to auto cherrypick to the stable-website branch after merging.