Add support for setting sendPreviousResourceOnDelete for FHIR store notification configs.

[modular-magician]

Fixes hashicorp/terraform-provider-google#15349.

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Release Note Template for Downstream PRs (will be copied)

healthcare: added `send_previous_resource_on_delete` field to `notification_configs` of `google_healthcare_fhir_store`

Derived from GoogleCloudPlatform/magic-modules#8507