feat: add support for multi region using new region field from aws provider v6

[Jno21]

This PR adds a backwards-compatible feature that simplifies deployment across multiple AWS regions by leveraging the new region argument capability introduced in AWS Provider v6.

Implementation

New optional variable: region

• Allows explicit control over which AWS region the Datadog Forwarder is deployed to
• When omitted, defaults to the provider's configured region (maintains backwards compatibility)
• Enables deploying multiple forwarder instances in different regions without provider aliasing

Tests

Add multi_region.tftest.hcl:

• test that region is properly set
• test that applies on different regions don't conflict (IAM roles, etc.)

terraform test

tests/default_config.tftest.hcl... in progress
  run "default_config_test"... pass
  run "environment_variables_test"... pass
tests/default_config.tftest.hcl... tearing down
tests/default_config.tftest.hcl... pass
tests/enhanced_features.tftest.hcl... in progress
  run "enhanced_features_test"... pass
  run "enhanced_features_env_vars_test"... pass
tests/enhanced_features.tftest.hcl... tearing down
tests/enhanced_features.tftest.hcl... pass
tests/existing_resources.tftest.hcl... in progress
  run "existing_resources_test"... pass
tests/existing_resources.tftest.hcl... tearing down
tests/existing_resources.tftest.hcl... pass
tests/multi_region.tftest.hcl... in progress
  run "multi_region_us_east_1"... pass
  run "multi_region_us_east_2"... pass
  run "multi_region_us_east_1_existing_resources"... pass
  run "multi_region_us_east_2_existing_resources"... pass
tests/multi_region.tftest.hcl... tearing down
tests/multi_region.tftest.hcl... pass
tests/optional_env_vars.tftest.hcl... in progress
  run "optional_env_vars_test"... pass
tests/optional_env_vars.tftest.hcl... tearing down
tests/optional_env_vars.tftest.hcl... pass
tests/vpc_config.tftest.hcl... in progress
  run "vpc_configuration_test"... pass
tests/vpc_config.tftest.hcl... tearing down
tests/vpc_config.tftest.hcl... pass

[RaphaelAllier]

Thanks for contribution ! We're reviewing this internally and will get back to you

[ktmq]

this is awesome, thanks so much @Jno21 ! we'll include this in v1.0.3 🙌