feat: Allow a more flexible module extension.

[olivierkessler]

Description

Allows using conditionals when extending this module to enable/disable features (replication, logging, inventory)

• Solves Issue 297

Motivation and Context

Basically we've been experiencing the same issue as the person in the aforementioned issue. We extend this module and need to enable/disable replication, logging and inventory using feature flags/variables.

This cannot be done in a single central child module (the one linked to this PR would be the parent), given that'd require a conditional with one side being a properly structured map and the other side being an empty map, which terraform doesn't seem to allow.

Impact : One option today for users is to deploy infrastructure for replication, logging and inventory, even if they don't need it. The other option is having N child modules on user side, for all combinations of (replication, logging, inventory).

Solution : Allowing those configurations to be nullable, does not break backward compatibility but enable users to have a single extended/child module that can be controlled via feature flags.

What does not work today :

module "child_module" {
  source  = "terraform-aws-modules/s3-bucket/aws"

   ...
  logging = var.enable_logging ? {
    target_bucket = var.logging_bucket_id
    target_prefix = "logs/${var.bucket_name}"
    target_object_key_format = {
      partitioned_prefix = {
        partition_date_source = "DeliveryTime"
      }
    }
  } : {}

What works thanks to this PR:

module "child_module" {
  source  = "terraform-aws-modules/s3-bucket/aws"

   ...
  logging = var.enable_logging ? {
    target_bucket = var.logging_bucket_id
    target_prefix = "logs/${var.bucket_name}"
    target_object_key_format = {
      partitioned_prefix = {
        partition_date_source = "DeliveryTime"
      }
    }
  } : null 

Breaking Changes

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request