feat: add vertexai embeddings (#2693)
This PR:
- Adds VertexAI embeddings as an embedding provider
Testing
- Tested with pinecone destination connector on
[this](https://github.com/Unstructured-IO/unstructured/actions/runs/8429035114/job/23082700074?pr=2693)
job run.
---------
Co-authored-by: Matt Robinson <mrobinson@unstructuredai.io>
Co-authored-by: Matt Robinson <mrobinson@unstructured.io>
