Google genai embeddings (#18079)

docs/docs/examples/embeddings/gemini.ipynb

docs/docs/examples/embeddings/google_genai.ipynb

docs/docs/examples/embeddings/google_palm.ipynb

...ations/embeddings/llama-index-embeddings-gemini/README.md

...embeddings/llama-index-embeddings-google-genai/.gitignore

...ions/embeddings/llama-index-embeddings-google-genai/BUILD

...ns/embeddings/llama-index-embeddings-google-genai/LICENSE

...s/embeddings/llama-index-embeddings-google-genai/Makefile

.../embeddings/llama-index-embeddings-google-genai/README.md

...gs-google-genai/llama_index/embeddings/google_genai/BUILD

...gle-genai/llama_index/embeddings/google_genai/__init__.py

...-google-genai/llama_index/embeddings/google_genai/base.py

...ddings/llama-index-embeddings-google-genai/pyproject.toml

...mbeddings/llama-index-embeddings-google-genai/tests/BUILD

...ngs/llama-index-embeddings-google-genai/tests/__init__.py

...x-embeddings-google-genai/tests/test_embeddings_gemini.py

...ations/embeddings/llama-index-embeddings-google/README.md