Revamp EKS Fargate documentation (#20144)

* Structural changes to order, pre-reqs (profile,keys,rbac), and add troubleshooting auth command

* Clarify context, prereqs, and agent sidecar setup

* Fix all subintegrations, links, raw API Key

* Fix some typos and eng notes

* edits

* post doc review updates

* Remove unnecessary containerPort step for DogStatsD/APM

* Fix non-ascii hyphen

* Update README.md

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Co-authored-by: cecilia saixue watt <cecilia.watt@datadoghq.com>
Co-authored-by: Steven Blumenthal <steven.blumenthal@datadoghq.com>

Author: 3 people