Replace var.account_id with aws_caller_identity in db_provision IAM policy

[sanjay20m]

This PR improves the Terraform configuration by replacing the use of the hardcoded var.account_id variable with the dynamic aws_caller_identity data source within the db_provision IAM policy. This update:

Aligns with Terraform best practices

Reduces required configuration variables

Improves portability and security

##Files Changed
terraform/modules/data-persistence/main.tf

CHANGELOG.md

##Related Changelog Entry
Under ## [Unreleased]:

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• CUMULUS-XXXX
  • Replaced use of var.account_id with the aws_caller_identity data source in the db_provision IAM policy to avoid requiring a hardcoded account ID in configuration. This improves portability and aligns with Terraform best practices.

[sanjay20m]

@Jkovarik any changes required now !!

[sanjay20m]

Hi @Jkovarik,
Just following up to see if this is ready for review. All updates have been made per guidelines, including the changelog entry and replacing var.account_id with aws_caller_identity for better portability and security.

Please let me know if anything else is needed. Thanks!