add configuration for exclude root module

[njuCZ]

waiting for PR: hashicorp/terraform-ls#251

[appilon]

hello @njuCZ,

We are working on better workspace support in #448 , it would make sense to pull your work in there, so I'm going to retarget your Pull Request and help get it across the finish line 👍

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the context necessary to investigate further.