Remove providers in legacy module

[davidholsgrove]

The specifying of provider configuration in a terraform module makes this a "legacy" component, and prevents the use of the module with conditional counts / for_each etc.

https://developer.hashicorp.com/terraform/language/modules/develop/providers#legacy-shared-modules-with-provider-configurations

Can this module be refactored to avoid this? It might require additional documentation on how a consumer of the module should provide the AWS providers

https://github.com/gofireflyio/terraform-firefly-aws-onboarding/blob/main/main.tf#L6-L403