add CLI argument --disable-workspace-trust (#5638)

Add CLI flag to disable workspace trust feature, as
described in documentation:
https://code.visualstudio.com/docs/editor/workspace-trust

Add test for workspace trust argument.

test/e2e/openHelpAbout.test.ts

@@ -1,7 +1,7 @@
 import { version } from "../../src/node/constants"
 import { describe, test, expect } from "./baseFixture"
 
-describe("Open Help > About", [], {}, () => {
+describe("Open Help > About", ["--disable-workspace-trust"], {}, () => {
   test("should see code-server version in about dialog", async ({ codeServerPage }) => {
     // Open using the menu.
     await codeServerPage.navigateMenus(["Help", "About"])