Update Terraform module to create the Firestore DB through a terraform resource

[bgood]

Looks like the App Engine Terraform resource can now create a Firestore db, so we should update the Autoscaler Terraform. This will clean up some steps in the deployment process and simplify the installation process.

Reference:
https://cloud.google.com/firestore/docs/solutions/automate-database-create#create_a_database_with_terraform
https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/app_engine_application