Undefined Flag Errors

Improved error messages for undefined flags

Detection has been added for scenarios when a user is using a flag that might be meant to be passed to OpenTofu/Terraform in the run command, and suggests using the -- argument to pass it through.

As an example:

$ terragrunt run providers lock -platform linux_amd64 -platform darwin_arm64
14:52:19.496 ERROR  flag `-platform` is not a Terragrunt flag. If this is an OpenTofu/Terraform flag, use `--` to forward it (e.g., `terragrunt run -- <command> -platform`).