Add notebook to quickly generate and load embeddings in AlloyDB.

[paulramsey]

Add AlloyDB Embeddings Notebook

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.12 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• Please merge this PR for me once it is approved

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[kurtisvg]

Some quick issues I see while reviewing:

P0s:

• The code is not tested (which is required to merge)
• Versions installed w/ pip should be pinned to prevent issues with updates
• We should update to load data from a file -- either a file in this repo or a public GCS bucket to streamline implementation

P1s:

• We should be using type hints
• User inputs should be streamlined to not rely on Secret Manager -- something like the "Set up alloyDB" section here would be preferred
• We should evaluate using asyncio -- much of this is blocked on I/O, may speed it up considerably to operate in parallel
• Need to evaluate failure for vertex AI quota issues

P2s:

• Should consider using a generator for a batching function (python best practice)
• We may also want to consider using the AlloyDB Python Connector here for mTLS + make execution in the codelab better

[glasnt]

Closed in favour of #12721