Make terraform_standard_module_structure configurable

[fatbasstard]

Introduction

Hi, it would be nice if the terraform_standard_module_structure rule can be made configurable. It currently checks the entire module structure (https://github.com/terraform-linters/tflint-ruleset-terraform/blob/v0.2.0/docs/rules/terraform_standard_module_structure.md#why).

It's an "all or nothing" rule ATM

In our case we've split out the outputs in multiple output files (for reasons), but this makes it impossible to use this rule. But we do like to use the rules for the other files (e.g. variables.tf)

Proposal

Add some options to tweak this rule, e.g. disable the check on outputs being defined in outputs.tf.

[marghidanu]

We want to extend our structure with additional files like providers.tf, versions.tf and it would be nice if we could specify additional files that would be required.

[madpipeline]

Just to add my scenario here: We use prefix our files with an _ so they are called _outputs.tf and _variables.tf amongst other files, for sorting purposes. When we have a lot of files within a module, having these at the top makes the interface of the module easy and quickly to find.

This is our reason for which we cannot use this rule at all.