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.

[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• ai-ml/llm-multi-cluster-gw/tgi-2b-it-1.1-eu.yaml:15, tag gke_ai_ml_llm_serving_gemma_tgi_2b_it_deployment
• ai-ml/llm-multi-cluster-gw/tgi-2b-it-1.1-us.yaml:15, tag gke_ai_ml_llm_serving_gemma_tgi_2b_it_deployment

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment