Doc updates for aws iam auth addition and removal

[snarkychef]

Issue #, if available:
https://github.com/aws/eks-anywhere-internal/issues/2455

Description of changes:
Documentation changes to reflect the newly added capabilities of addition or deletion of aws iam authentication to an existing cluster using upgrade workflows. Relevant code changes in #9897

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.01%. Comparing base (2b32936) to head (f92c170).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9978   +/-   ##
=======================================
  Coverage   70.01%   70.01%           
=======================================
  Files         680      680           
  Lines       41748    41748           
=======================================
  Hits        29230    29230           
  Misses      10721    10721           
  Partials     1797     1797           

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[sp1999]

/lgtm

[snarkychef]

/approve

[snarkychef]

/cherry-pick release-0.24

[eks-distro-pr-bot]

@snarkychef: once the present PR merges, I will cherry-pick it on top of release-0.24 in a new PR and assign it to you.

In response to this:

/cherry-pick release-0.24

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[eks-distro-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: snarkychef

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• docs/OWNERS [snarkychef]

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[eks-distro-pr-bot]

@snarkychef: new pull request created: #10320

In response to this:

/cherry-pick release-0.24

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.