fix: simplified vertex plugin APIs

[pavelgj]

   vertexAIModelGarden({
      location: 'us-central1',
      models: [claude3Sonnet, llama31],
    }),
    vertexAIEvaluation({
      location: 'us-central1',
      metrics: [
        VertexAIEvaluationMetricType.BLEU,
        VertexAIEvaluationMetricType.GROUNDEDNESS,
        VertexAIEvaluationMetricType.SAFETY,
        {
          type: VertexAIEvaluationMetricType.ROUGE,
          metricSpec: {
            rougeType: 'rougeLsum',
            useStemmer: true,
            splitSummaries: 'true',
          },
        },
      ],
    }),
    vertexAIRerankers({
      projectId: PROJECT_ID,
      location: LOCATION,
      rerankers: ['vertexai/reranker'],
    }),

[cabljac]

lgtm