Update clusterLocal docs to allow for exceptions when using wide clusterLocal configs

[clarkjohnd]

Description

Updates documentation related to clusterLocal changes made here (istio/istio#52367) and backported to 1.22 and 1.23.

Changes are simple, can now set wider services/namespaces/global as clusterLocal, and then set more refined services and namespaces contained in the clusterLocal config to not be clusterLocal, allowing us to stop sharing all but certain services.

Reviewers

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• Docs
• Installation
• Networking
• Performance and Scalability
• Extensions and Telemetry
• Security
• Test and Release
• User Experience
• Developer Infrastructure
• Localization/Translation

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[istio-testing]

Hi @clarkjohnd. Thanks for your PR.

I'm waiting for a istio member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[windsonsea]

/ok-to-test

[clarkjohnd]

Relevant section: https://deploy-preview-15828--preliminary-istio.netlify.app/latest/docs/ops/configuration/traffic-management/multicluster/#keeping-traffic-in-cluster