Backport of [NET-4122] Doc guidance for federation with externalServers into release/1.15.x#18232

hc-github-team-consul-core merged 1 commit intorelease/1.15.xhashicorp/consul:release/1.15.xfrom

backport/zalimeni/net-4122-externalservers-wanfed-k8sauthmethodhost-guidance/primarily-probable-pipefishhashicorp/consul:backport/zalimeni/net-4122-externalservers-wanfed-k8sauthmethodhost-guidance/primarily-probable-pipefishCopy head branch name to clipboard