first pass at MongoDB Atlas via AWS

[rkhullar]

Description

This PR starts support for the MongoDB provider. The construct supports creating either a shared or serverless single region Atlas cluster backed by AWS. And the access module manages network and permissions for the cluster.

Future Work

• add example usage
• support dedicated clusters
• troubleshoot or add note for create_admin variable

Additional Notes

The access_rules are meant to reference IAM role names within a project. For example, if you use "fastapi-lambda" as the role name in the rule, that could reference "${var.project}-fastapi-lambda-{var.environment}-${var.namespace}" depending on your naming convention. I was looking to implement, but it doesn't seem like that's supported. Terraform has a templatefile but not an equivalent function for working with in memory string templates. And there is a data source with the template provider but that has been deprecated in favor of the templatefile function.

• https://developer.hashicorp.com/terraform/language/functions/templatefile
• https://registry.terraform.io/providers/hashicorp/template/latest/docs
• Introduce a template() function that works on string content hashicorp/terraform#30616