EKU Update to explain client and server auth

[Joe-Winchester]

Describe your pull request here:

Following a customer issue with zowe 3.5 and the introduction of the zowe.certificate.keystore.clientCertificateAlias property, updating the docs to discuss the removal of dual use EKU.

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[github-actions]

📁 The PR description is missing the file name(s) for the updated content. List all the files included in this PR so this information displays in our Zowe Docs GitHub Slack channel.

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📌 The subject area label is missing. Add an area: label so we know what your content is about.

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🔍 The review label is missing. Add a review: label so we can determine who needs to approve this PR.

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💾 The release label is missing. Add a release: label so your content is published with the correct major Zowe release.

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