serverlessv2_scaling_configuration does not imply instance class

[paulerickson]

Describe the Bug

serverlessv2_scaling_configuration is a cluster attribute—which can never be unset, by the way—required to add db.serverless instances to a provisioned cluster, but it does not imply that that there must be any serverless instances.

This conditional would give every instance class db.serverless, even if instance_type is set to another value.

Expected Behavior

instance_type var configures the instance_class attribute of aws_rds_cluster_instance resources.

Steps to Reproduce

1. Set instance_type to some provisioned instance type
2. Set serverlessv2_scaling_configuration to something non-null
3. aws_rds_cluster_instance resource instance_class changes to db.serverless ☹️

Screenshots

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Environment

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Additional Context

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[frimik]

Same. Causes issues in various transitions or mixes of db.serverless and other regular "provisioned" instances.