Adding missing fields to vertexai.Endpoint resource

[modular-magician]

Fixes hashicorp/terraform-provider-google#19995

We were missing a few fields so I added them. enable_private_service_connect is deprecated and seems to always return "false" now, so I'm skipping it.

traffic_split can't actually be set on resource creation, you need to "deploy" a model associated with the endpoint, and you need to have deployed a model in order to get the keys in the map. I think traffic_split only applies to the new config I'm enabling here, so it's hard to test anyway.

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vertexai: added `traffic_split`, `private_service_connect_config`, `predict_request_response_logging_config`, `dedicated_endpoint_enabled`, and `dedicated_endpoint_dns` fields to `google_vertex_ai_endpoint` resource

Derived from GoogleCloudPlatform/magic-modules#12110