LSP path doesn't recognise `${workspaceFolder}`

[coderfromhere]

Hi, the extension setting does not recognise VS Code variables like ${workspaceFolder} in LSP path field. I'm using a similar setting in Haskell Language Server to point to a HLS instance from a Nix shell (${workspaceFolder}/hls.exe which is a symlink for a /nix/... path), and the same variables are expanded correctly there but not in the dhall extension.