feat: update versionmanager to support root.hcl files

[edgar-castle]

Context

When running plan/applies in newer versions of terragrunt, you now get the following output when the root configuration file is named terragrunt.hcl.

WARN[0000] Using `terragrunt.hcl` as the root of Terragrunt configurations is an anti-pattern, and no longer recommended. 
In a future version of Terragrunt, this will result in an error. You are advised to use a differently named file like `root.hcl` instead.
For more information, see https://terragrunt.gruntwork.io/docs/migrate/migrating-from-root-terragrunt-hcl

Gruntwork now recommends renaming the root config file to root.hcl instead. This PR is to add support for the new recommended naming convention in versionmanager.

Motivation

We've been doing some testing around using tenv to aid with Terraform & Terragrunt version management in our CI pipelines. Some repos use the new root.hcl format and tenv wasn't parsing terraform_version_constraint and
terragrunt_version_constraint since the file was named differently.

I first thought of setting an env var to pass in a different root terragrunt file name instead to make this more customizable. However, most people will likely conform to rename the file using whatever GruntWorks recommends so I figured adding support for the most likely cases was the better approach. It makes using the tool even easier since out of the box it will work with the most common configurations.

Summary of Change

The changes I made should be backwards compatible without changing anyone's current setup.
The following was done:

1. I updated the consts in gruntparser.go with 2 new consts HCLNameLegacy and JSONNameLegacy and added some Go Doc compliant comments to indicate the move towards the new recommended naming convention.
2. Added in new VersionFile configs in the tf, tg, and tofu BuildManager functions to now include parsing of the root.hcl & root.hcl.json files in the returned VersionManager struct.
   • I placed it after the terragrunt.hcl and terragrunt.hcl.json parser declarations to ensure this wouldn't break anyone's current setup using the legacy naming convention. So if they have both a terragrunt.hcl file and root.hcl file, the terragrunt.hcl file values will be the ones parsed and utilized.

Testing

I built the binaries then tested out the logic to ensure that it is correctly parsing the legacy and newly named files. I also ensured that the legacy file name takes precedence over the new one.

Terraform Detect Tests

Terragrunt Detect Test

Tofu Detect Test

[kvendingoldo]

Wow! Looks amazing! LGTM

[kvendingoldo]

Thank you for the contribution, @edgar-castle! I gonna merge it, and make a release.

[edgar-castle]

Sweeeet, happy to help! 😃