fix(vertexai): use correct API URL for global location

[janplancraft]

Fixes the Vertex AI plugin to use https://aiplatform.googleapis.com instead of https://global-aiplatform.googleapis.com when location: 'global' is specified.

Fixes #3651

Changes:

• list-models.ts - Model listing endpoint
• predict.ts - Predict endpoint
• upsert_datapoints.ts - Vector search upsert endpoint
• evaluator_factory.ts - Evaluation endpoint
• model_garden.ts (legacy) - Model garden template URL
• llama.ts (v2) - Llama model template URL

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