Add custom Vertex AI Model Garden example

[stefannae]

This PR adds an example of how to use models besides Gemini from the Vertex AI Model Garden.

• Fixes Vertex Model garden models #960.

[DouweM]

Would just publishers/meta/models/llama-3.3-70b-instruct-maas work as the project and location have already been configured?

[stefannae]

Yes. All these patterns should work:

f`{model_id}`,
f`publishers/{publisher}/models/{model_id}`,
f`projects/{project}/locations/{location}/publishers/{publisher}/models/{model_id}`

which is aligned with:
https://googleapis.github.io/python-genai/genai.html#genai.models.AsyncModels.generate_content_stream

Should I use the partial resource name publishers/meta/models/llama-3.3-70b-instruct-maas?

[DouweM]

@stefannae Yeah, let's use the simplest option that doesn't require additional variables

[stefannae]

@DouweM okay, made the change

[github-actions]

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[DouweM]

From googleapis.github.io/python-genai/genai.html#genai.models.AsyncModels.generate_content_stream, it seems like this should be meta/llama-3.3-70b-instruct-maas, so we should fix it here and specify {publisher}/{model_id} in the docs above.

[stefannae]

I missed this 4th way of specifying the model. Still, the simplest way, according to the same docs (and tested - I've tested them all), is llama-3.3-70b-instruct-maas.

Should we keep llama-3.3-70b-instruct-maas in the example and add {publisher}/{model_id} to the list of patterns?

[DouweM]

@stefannae Hmm, the docs make it sound like excluding the publisher only works with Gemini models, so even though you've verified it works with llama as well, I'd prefer to document and use only {publisher}/{model_id}, or say "{model_id} for Gemini models" like the docs do.

[stefannae]

@DouweM, they have a formatting issue with the docs, which visually reads better from the docstring https://github.com/googleapis/python-genai/blob/538c755e84777e6b76d5152aac18268e4d0c99c6/google/genai/models.py#L6377-L6401

This way, seems Gemini is only used as an example:

For the `model` parameter, supported formats for Vertex AI API include:
- The Gemini model ID, for example: 'gemini-2.0-flash'
- The full resource name starts with 'projects/', for example:
  'projects/my-project-id/locations/us-central1/publishers/google/models/gemini-2.0-flash'
- The partial resource name with 'publishers/', for example:
  'publishers/google/models/gemini-2.0-flash' or
- `/` separated publisher and model name, for example:
  'google/gemini-2.0-flash'

For the `model` parameter, supported formats for Gemini API include:
- The Gemini model ID, for example: 'gemini-2.0-flash'
- The model name starts with 'models/', for example:
  'models/gemini-2.0-flash'
- For tuned models, the model name starts with 'tunedModels/',
  for example:
  'tunedModels/1234567890123456789'

Though given how the endpoints are defined in Vertex AI, it is probably better to switch to {publisher}/{model_id} in the example. Let me know your preference, and I'll make the change.

[DouweM]

@stefannae Yeah let's do that, I'm interpreting "Gemini model ID" as "this only works for Gemini models"

[stefannae]

@DouweM ok, pushed the update!

[DouweM]

@stefannae Thanks Stefan, should merge shortly!