Resvise the way to launch nodegroup for AWS Outposts

[0xlen]

Issue #, if available:

The current steps in the documentation is using AWS CLI command to create EKS cluster, however, due to the EKS cluster was not created and managed by eksctl, the eksctl need to look up CloudFormation stack with specific tag/suffix to get cluster configuration(#L189-L209). In this case, eksctl might report error(no eksctl-managed CloudFormation stacks found for <...>) when trying to create nodegroup for that cluster out of its control, as below:

❯ ./eksctl create nodegroup --cluster myOutPostCluster --name myOutPostCluster-nodes --node-type c5.xlarge .... --region us-west-2
[ℹ]  eksctl version 0.30.0-rc.1
[ℹ]  using region us-west-2
[ℹ]  will use version 1.18 for new nodegroup(s) based on control plane version
Error: getting existing configuration for cluster "myOutPostCluster": no eksctl-managed CloudFormation stacks found for "myOutPostCluster"

• See: no eksctl-managed CloudFormation stacks found eksctl-io/eksctl#877

Description of changes:

Change it to use CloudFormation template to launch self-managed nodegroup. But I don't have outpost environment, need to verify to see if this is correct.

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[jimdial-aws]

I removed the procedural instructions from the Outposts topic. It now references the create cluster and self-managed nodes topics, which have been updated with the correction instructions for Outposts.