add option for enabling global write forwarding

[tdockseydt]

what

Add option for enabling global write forwarding for aws rds cluster.

why

• Ability to enable global write forwarding across our aws rds clusters.
• https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/aurora-global-database-write-forwarding-apg.html
• https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/rds_cluster#enable_global_write_forwarding

[hans-d]

/terratest

[hans-d]

@tdockseydt

README.md is outdated. Please run the following commands locally and push the file:
make init
make readme
Error: Process completed with exit code 1.

[mergify]

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[mergify]

💥 This pull request now has conflicts. Could you fix it @tdockseydt? 🙏

[osterman]

/terratest

[osterman]

/terratest