Add assume-role-arn option to update-kubeconfig command for cross-account access

[sdomme]

Issue #, if available: #8554

This PR supersedes #9364

Description of changes:

This change introduces support for assuming an IAM role when retrieving cluster information in the update-kubeconfig command. By specifying the --assume-role-arn argument, users can assume a cross-account IAM role to access cluster details. The implementation updates the EKSClient to handle role assumption using the AWS STS service and injects the temporary credentials into the EKS client configuration. This enhancement improves cross-account compatibility and simplifies cluster management in multi-account environments.

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[aemous]

@sdomme Can you please run ./scripts/new-change and commit a new changelog entry using the configuration below before we merge it?

{
  "type": "feature",
  "category": "``eks``",
  "description": "Add assume-role-arn option to update-kubeconfig command for cross-account access"
}

The resulting file should be identical to this one.

[sdomme]

@aemous Does the name of the files also need to be identical? Because I got one generated with a different name.

[aemous]

@aemous Does the name of the files also need to be identical? Because I got one generated with a different name.

The file names can be different

[AndrewAsseily]

Hi @sdomme,

1. Could you update the parameter description as you see fit or verify that no changes to the description are necessary: https://docs.aws.amazon.com/cli/latest/reference/eks/update-kubeconfig.html
   (Note that our docs generation will automatically handle the Options section documentation.)
2. Would you consider adding an example of the new argument to our update-kubeconfig examples? While not required, it would be a valuable addition for customers. If you do add an example, please ensure it follows our example style guide.

EDIT: Approving this PR otherwise.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.39%. Comparing base (5f07db1) to head (b54856e).
Report is 78 commits behind head on develop.

Files with missing lines	Patch %	Lines
awscli/customizations/eks/update_kubeconfig.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #9443   +/-   ##
========================================
  Coverage    93.39%   93.39%           
========================================
  Files          210      210           
  Lines        16983    16993   +10     
========================================
+ Hits         15861    15871   +10     
  Misses        1122     1122           

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