[Bug]: Restore HCL language

[alexeagle]

What happened?

Switched from hcl to terraform because terraform-fmt doesn't cover everything

See comment:

rules_lint/format/private/format.sh

Lines 58 to 63 in a9d300f

	# Note: terraform fmt cannot handle all HCL files such as .terraform.lock
	# "Only .tf and .tfvars files can be processed with terraform fmt"
	# so we define a custom language here instead of 'HCL' from github-linguist definition for the language.
	# TODO: we should probably use https://terragrunt.gruntwork.io/docs/reference/cli-options/#hclfmt instead
	# which does support the entire HCL language FWICT
	'Terraform') patterns=('*.tf' '*.tfvars') ;;

[alexeagle]

Some research:

I was wrong about https://terragrunt.gruntwork.io/docs/reference/cli-options/#hclfmt - it only wants to format "terragrunt" files, none of the HCL files in Silo were affected by it. Dead end.

The official HCL language does provide a formatter, however they don't ship any binary distribution.
https://github.com/hashicorp/hcl/blob/main/cmd/hclfmt/main.go

According to one of the HCL2 authors, each product that uses HCL actually ships its own fmt command intentionally because the domain-specifics may be formatted beyond what the language syntax understands:
hashicorp/vscode-hcl#98 (comment)

So that means users of rules_lint might expect their vault files to be vault fmt, packer files to be packer fmt, terraform to be terraform fmt, etc. This strikes me as a lot of burden for a little repo like this to take on.

Or, we can eschew these domain-specifics and just run the generic hclfmt, providing less value than those users expect, as they might take a file that's already "correctly formatted" according to rules_lint, run terraform fmt on it, and then be surprised that it makes modifications. In this case we'd also want to provide a precompiled binary to make things easier for users.

[alexeagle]

Slipping this from 1.0, it looks too underspecified