Backport of [NET-4122] Doc guidance for federation with externalServers into release/1.1.x#2605

hc-github-team-consul-core merged 1 commit intorelease/1.1.xhashicorp/consul-k8s:release/1.1.xfrom

backport/zalimeni/net-4122-externalservers-wanfed-k8sauthmethodhost-guidance/likely-lenient-geckohashicorp/consul-k8s:backport/zalimeni/net-4122-externalservers-wanfed-k8sauthmethodhost-guidance/likely-lenient-geckoCopy head branch name to clipboard