Backfill support for user_project_override and billing_project for google_service_networking_connection

[modular-magician]

Fixes: hashicorp/terraform-provider-google#9466

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Release Note Template for Downstream PRs (will be copied)

servicenetworking: added support for `user_project_override` and `billing_project ` to `google_service_networking_connection`

Derived from GoogleCloudPlatform/magic-modules#4995