fix: Add explicit default value for engine_mode used in conditiona logic internally

[pdeva]

sets default value for engine_mode var as is in the description

Description

sets default value for engine_mode.

Motivation and Context

without this, if engine_mode is not specified, serverlessv2_scaling_configuration will not take effect since it expects an actual value of provisioned in engine_mode

Breaking Changes

None

How Has This Been Tested?

• [ x] I have updated at least one of the examples/* to demonstrate and validate my change(s)
• [x ] I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request

[bryantbiggs]

Can you provide more details and a reproduction as to the issue you are facing? This is the default value that is specified by the provider https://github.com/hashicorp/terraform-provider-aws/blob/d9290535ae088a600ddec41fe63e899185d74b56/internal/service/rds/cluster.go#L181

[pdeva]

this line

terraform-aws-rds-aurora/main.tf

Line 136 in 973666e

for_each = length(var.serverlessv2_scaling_configuration) > 0 && var.engine_mode == "provisioned" ? [var.serverlessv2_scaling_configuration] : []

is not triggered if an explicit value is not specified for engine_mode

[bryantbiggs]

thank you - that makes a lot more sense now and I agree, this value is necessary to support that logic

[github-actions]

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[antonbabenko]

This PR is included in version 7.6.2 🎉

[github-actions]

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