Add TF_HOME_DIR env variable support as alternative to ~/.terraform.d

[tony-sol]

Add supporting for TF_HOME_DIR environment variable for unix, which allows to move terraform.d dir from $HOME.

If TF_HOME_DIR is empty or not set, fallback to default behavior with ~/.terraform.d

Fixes #15389

Target Release

1.4.x

Draft CHANGELOG entry

NEW FEATURES

• You can now specify alternative to ~/.terraform.d config directory location with TF_HOME_DIR. Default config file affected as well - with TF_HOME_DIR it will be placed in "${TF_HOME_DIR}/terraformrc" if not overwritten by TF_CLI_CONFIG_FILE or TERRAFORM_CONFIG

[hashicorp-cla]

All committers have signed the CLA.

[crw]

Thanks for your submission! The feedback on this PR from the maintainers is that we would rather not invent a new Terraform-specific environment variable when there's already a standard on each of the primary platforms we target. Thus we would be more interested in supporting the XDG specification (and its equivalents on macOS and Windows).

The hope was to address this with other (possibly breaking) changes to CLI configuration, e.g. HCL 2 support for CLI config, however that does not seem likely in the near future. I will keep this PR open for now pending further discussion of the solution. Thanks again for this submission! We appreciate your contribution.

[tony-sol]

Closed due to make a more complex solution

[github-actions]

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