feat(vertexai): add parameter region to google_vertex_ai_featurestore_entitytype_feature

[modular-magician]

fixes #13217.

This PR will make google_vertex_ai_featurestore_entitytype_feature always use regional endpoint corresponding to parent's region. This will prevent the error: "Cannot determine region: set in this resource, or set provider-level 'region' or 'zone'" from happening.

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Release Note Template for Downstream PRs (will be copied)

vertexai: made google_vertex_ai_featurestore_entitytype_feature always use regional corresponding to parent's region

Derived from GoogleCloudPlatform/magic-modules#6992

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