Use substring check for EKS cluster name provider

[therealdwright]

Summary of your changes

Karpenter managed clusters will use aws:eks:cluster-name for its
cluster name tag. This commit updates the logic to use a substring
check so both the existing tag of eks:cluster-name and karpenter
are supported.

Related Issues

• Fixes: Cloudbeat failed to get cluster name when using Karpenter #2226

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary README/documentation (if appropriate)

[mergify]

This pull request does not have a backport label. Could you fix it @therealdwright? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 8./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[github-actions]

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[moukoublen]

Hello @therealdwright, and thanks for opening the issue and the PR,

One minor concern: Would it be safer to compare using ends with instead of contains?

I am not sure if it's actually needed. I just thought of cases where tags could perhaps contain eks:cluster-name in the name but refer to a different thing.

[therealdwright]

I think this is a fair criticism and I am only personally interested in ends with but was trying to be robust but happy to boil this one down to YAGNI.

[moukoublen]

LGTM

Thanks @therealdwright!

[therealdwright]

Thanks @moukoublen - would you have any idea which elastic-agent release this will be in?

[moukoublen]

@therealdwright most probably 8.15.0.