Migrate away from the deprecated list function

[kjagiello]

Now that Terraform 0.15 is released, I've run into some issues with this module as it is using a function that got removed, namely list. This PR replaces it with tolist.

Error from Terraform 0.15 for reference:

│ Error: Error in function call
│ 
│   on .terraform/modules/default_label/main.tf line 2, in locals:
│    2:   original_tags    = join(var.delimiter, compact(concat(list(var.namespace, var.stage, var.name), var.attributes)))
│     ├────────────────
│     │ var.name is a string, known only after apply
│     │ var.namespace is a string, known only after apply
│     │ var.stage is a string, known only after apply
│ 
│ Call to function "list" failed: the "list" function was deprecated in
│ Terraform v0.12 and is no longer available; use tolist([ ... ]) syntax to
│ write a literal list.

[Gowiem]

/test all

[Gowiem]

@kjagiello any reason you're using this module over the terraform-null-label module?

[kjagiello]

Haven't actually seen it before. Will take a look, thanks!

[Gowiem]

@kjagiello that's the main label module that I would suggest you use. This one is out of date and I believe it should be archived. I have brought that up with the rest of the Cloud Posse team, so you may see this module get archived in favor of the terraform-null-label module since that is where we're putting our effort nowadays.

[kjagiello]

I'll look into migrating away then. Thanks for the clarification!