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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[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.

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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

[clarkjohnd]

@windsonsea hey, any movement on this? It's now released on latest versions of 1.22, 1.23 and 1.24 so keen to get the docs updated. Thanks

[windsonsea]

/lgtm for the text.

May need a technical review.