ci: rename vsix displayName to "Terragrunt Language Server (Official)" (#121)

The v0.0.2 publish failed with "This extension display name is taken"
because "Terragrunt Language Server" is already registered by another
Marketplace publisher (BahramJoharshamshiri.hcl-lsp).

Marketplace display names must be globally unique. Disambiguating with
"(Official)" to make it clear this is the Gruntwork-published extension.

Author: diofeher

vscode-extension/package.json

@@ -1,6 +1,6 @@
 {
 	"name": "terragrunt-ls",
-	"displayName": "Terragrunt Language Server",
+	"displayName": "Terragrunt Language Server (Official)",
 	"description": "Official Terragrunt Language Server extension by Gruntwork",
 	"author": "Gruntwork",
 	"license": "MPL-2.0",