feat: show info message in test extension

We want to know when the extension loads so we can check in the e2e
test.

Author: jsjoeio

test/e2e/extensions/test-extension/extension.ts

@@ -1,6 +1,7 @@
 import * as vscode from "vscode"
 
 export function activate(context: vscode.ExtensionContext) {
+  vscode.window.showInformationMessage("test extension loaded")
   context.subscriptions.push(
     vscode.commands.registerCommand("codeServerTest.proxyUri", () => {
       if (process.env.VSCODE_PROXY_URI) {