Vertex AI [Feature] support Part.from_uri for non-image files

[stevenaldinger]

I'm happy to contribute to the repo btw after getting validation that this makes sense as a feature.

I want to be able to upload text files once and be able to reference them.

Part.from_uri is only referenced in image utils here: libs/vertexai/langchain_google_vertexai/_image_utils.py#L80-L97

but in the vertexai module, that supports arbitrary mime types like the following example.

import vertexai
from vertexai.generative_models import GenerativeModel, Part

gemini_model = GenerativeModel(model_name="gemini-1.5-pro-preview-0409")

model_response = gemini_model.generate_content([
   "summarize the readme",
   Part.from_uri("gs://example-bucket/some-directory/README.md", "text/markdown"),
])

print(model_response)

[lkuligin]

sure, please, feel free to contribute. that would be a great addition!