Fix tag value validation and comprehensive tag merging with filtering for Aurora module

• Merge all relevant tag maps from tags_convention module (rds_tags, resource_tags, account_tags) with any additional root-level tags.

locals {
    combined_tags = merge(
         module.tags_convention.rds_tags,
         module.tags_convention.resource_tags,
         module.tags_convention.account_tags,
         var.tags
    )
}

• Filter out null or empty string tag values before passing to the Aurora module to prevent AWS API errors.
• Ensure single tags argument usage on the rds_aurora module call with the cleaned tag map.

Aurora Module:

module "rds_aurora" {
    source = "github.com/terraform-aws-modules/terraform-aws-rds-aurora?ref=v9.13.0"
    # tags = merge(module.tags_convention.resource_tags, var.tags)
    tags = merge(local.combined_tags,var.tags)
    ...
}

• Ensure internal usage of tags_convention module with proper input variable passing.
• Use similar safe tag merging pattern to filter out invalid tag values before resource application.

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Testing:

• Verified terraform plan and apply do not fail due to missing locals or empty tag values.
• Confirmed tags applied only include valid key-value pairs, excluding null or whitespace.
• Validated that no references to locals as a resource exist.

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Rationale:

• AWS forbids tag values that are empty or blank.
• Terraform locals need to be referenced with local, not locals.
• Properly filtering tags improves stability of infrastructure deployment.
• Consolidated locals and clean tag merges increase maintainability and reduce errors.

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Recommendations:

• Add validation rules to input variables where feasible to enforce tag integrity.