Add locality failover example to the ambient multicluster docs

[krinkinmu]

Description

This example requires changes introduced in #58065 and #57963. These PRs enable waypoints to route requests to remote network via ambient E/W gateway (using double HBONE). It's all required to address #57537.

With those changes in we can extend the initial multicluster setup example to show how to configure locality failover and along the way demonstrate how to deploy waypoints in multicluster ambient environments.

Reviewers

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

+cc @therealmitchconnors @keithmattix @Stevenjin8 @jaellio @mikemorris

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[keithmattix]

A couple of wording suggestions but other than that LGTM (assuming tests pass)

[krinkinmu]

/test doc.test.multicluster

[istio-testing]

@krinkinmu: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
doc.test.multicluster_istio.io	1cf9093	link	true	/test doc.test.multicluster

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[Stevenjin8]

did a quick read over, lgtm