feat: Add option to create/delete NAT Gateway route for private route tables

[ixolt]

Description

This update introduces a new variable, create_private_nat_gateway_route, to control the creation of NAT Gateway routes for private subnets. By making the creation of the aws_route.private_nat_gateway resource conditional, we provide users the flexibility to manage routes more precisely according to their specific requirements.

Key Changes:

• New Variable - create_private_nat_gateway_route (Boolean)
  • When set to true(default): NAT Gateway routes for private subnets are created automatically.
  • When set to false: NAT Gateway routes are not created, allowing users to define routes manually.
• Resource Modification - The aws_route.private_nat_gateway resource now checks the value of create_private_nat_gateway_route before creating routes.
• Use Case
  • Users can deploy NAT Gateways without setting automatic routes. This is particularly beneficial when a different routing strategy is in place, such as using a Transit Gateway for the default 0.0.0.0/0 route while assigning NAT Gateway routes only for specific destinations.

Example Use Case:

• If a Transit Gateway is used for the default 0.0.0.0/0 route and NAT Gateways are desired only for specific CIDR blocks, setting create_private_nat_gateway_route to false will prevent automatic route creation, giving full manual control over route configurations.

Motivation and Context

The change is required to provide greater flexibility and control over the infrastructure setup. Previously, creating a NAT Gateway would always result in the automatic creation of routes, which limited configuration options for complex setups. By introducing this conditional variable, users can decide whether or not to create NAT Gateway routes, making the module more adaptable to different networking requirements.
This enhancement addresses scenarios where automatic route creation is not desirable or conflicts with specific routing strategies.

• This module, doesnt integrate with the Network Firewall Module #978

Breaking Changes

No, this change does not break backward compatibility. The default behavior remains unchanged unless the create_private_nat_gateway_route variable is explicitly set to false.

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 deployed an example project with and without the create_private_nat_gateway_route variable set to ensure correct behavior.
  • Verified that the NAT Gateway routes are only deleted when the variable is disabled.
• I have executed pre-commit run -a on my pull request to ensure code quality and compliance with standards.

[antonbabenko]

This PR is included in version 5.15.0 🎉

[github-actions]

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