WIP: Multi-cluster LLM deployment

[TarasRudko]

Description

This PR adds sample of using multi-cluster Gateway to route traffic to LLM inference servers deployed on clusters in multiple regions

Tasks

• [ ] The contributing guide has been read and followed.
• [ ] The samples added / modified have been fully tested.
• [ ] Workflow files have been added / modified, if applicable.
• [ ] Region tags have been properly added, if new samples.
• [ ] All dependencies are set to up-to-date versions, as applicable.