Update Feature Store Region Availability Information

[jieshi1010]

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This PR updates documentation to reflect the expanded regional availability of Vertex AI Feature Store, as outlined in the official Google Cloud documentation: https://cloud.google.com/vertex-ai/docs/general/locations. Added the newly supported regions to the documentation. Tested region us-east4 in Colab without encountering any issues.

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[gericdong]

/gcbrun

[jieshi1010]

Sorry, my first time submitting a PR to this repo. What is blocking the merging now? @gericdong

[gericdong]

@jieshi1010: it looks good. Merged.