add vertexai/featureonlinestore resource (#9632) (#6789)

* rebase featureonlinestore based on merged changes

* rebase based on merged featureonlinestore pr

* fix pr suggestions featureonlinestore

* fix documentation and pr comments featureonlinestore
[upstream:f6b6532046e9886815386703ebdbfc9cfbcada93]

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/9632.txt

@@ -0,0 +1,9 @@
+```release-note:enhancement
+vertexai: added `force_destroy` field to `google_vertex_ai_feature_online_store` resource
+```
+```release-note:enhancement
+vertexai: added `optimized`, `dedicated_serving_endpoint` and `embedding_management` fields to `google_vertex_ai_feature_online_store` resource (beta)
+```
+```release-note:bug
+vertexai: changed `region` field from required to optional in `google_vertex_ai_feature_online_store` resource
+```