Support specifying the config location manually (outside of the user's profile) (#1921)

* Add support for loading the config from a given config location.

* Support using an env variable too.

* Add docs.

* Add test for configuration arguments

* remove .only

playwright/e2e/launch/config-options.spec.ts

@@ -0,0 +1,41 @@
+/*
+Copyright 2024 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { resolve } from "node:path";
+
+import { test, expect } from "../../element-desktop-test";
+
+test.describe("App config options", () => {
+    test.describe("Should load custom config via env", () => {
+        test.slow();
+        test.use({
+            extraEnv: {
+                ELEMENT_DESKTOP_CONFIG_JSON: resolve(__dirname, "../..", "fixtures/custom-config.json"),
+            },
+        });
+        test("should launch and use configured homeserver", async ({ page }) => {
+            await page.locator("#matrixchat").waitFor();
+            await page.locator(".mx_Welcome").waitFor();
+            await expect(page).toHaveURL("vector://vector/webapp/#/welcome");
+            await page.getByText("Sign in").click();
+            await page.getByText("matrix.example.org", { exact: true }).waitFor();
+        });
+    });
+    test.describe("Should load custom config via argument", () => {
+        test.slow();
+        test.use({
+            extraArgs: ["--config", resolve(__dirname, "../..", "fixtures/custom-config.json")],
+        });
+        test("should launch and use configured homeserver", async ({ page }) => {
+            await page.locator("#matrixchat").waitFor();
+            await page.locator(".mx_Welcome").waitFor();
+            await expect(page).toHaveURL("vector://vector/webapp/#/welcome");
+            await page.getByText("Sign in").click();
+            await page.getByText("matrix.example.org", { exact: true }).waitFor();
+        });
+    });
+});