fix: added parameter region to google_vertex_ai_featurestore_entitytype

[modular-magician]

fixes #10100 : "google_vertex_ai_featurestore_entitytype: Cannot determine region: set in this resource, or set provider-level 'region' or 'zone' #10100.

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Release Note Template for Downstream PRs (will be copied)

vertex_ai:  made google_vertex_ai_featurestore_entitytype always use regional endpoint corresponding to parent's region

Derived from GoogleCloudPlatform/magic-modules#6588

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