Added flags helper for Acceptance Tests in AdminX (#18500)

refs https://ghost.slack.com/archives/C0568LN2CGJ/p1696495250115289

Adds a new helper function `toggleLabsFlag` that allows toggling of lab
flags within tests. This function can be used directly inside a test
case or within `beforeEach` or `beforeAll` hooks to set the initial
state before tests run.

Usage:
- To toggle a flag within a test: `toggleLabsFlag('recommendations',
false);`
- To set initial state in a hook: 
  ```javascript
  beforeEach(() => {
    toggleLabsFlag('recommendations', true);
  });

---

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### <samp>🤖 Generated by Copilot at e138d58</samp>

This change adds a utility module for acceptance testing of experimental
features in Ghost. It allows tests to mock and change the labs settings
using `defaultLabFlags` and `toggleLabsFlag`.

apps/admin-x-settings/test/utils/acceptance.ts

@@ -47,6 +47,74 @@ export const responseFixtures = {
     latestPost: {posts: [{id: '1', url: `${siteFixture.site.url}/test-post/`}]}
 };
 
+let defaultLabFlags = {
+    adminXSettings: false,
+    recommendations: false,
+    audienceFeedback: false,
+    collections: false,
+    themeErrorsNotification: false,
+    outboundLinkTagging: false,
+    announcementBar: false,
+    signupForm: false,
+    lexicalEditor: false,
+    members: false
+};
+
+// Inject defaultLabFlags into responseFixtures.settings and config
+let labsSetting = responseFixtures.settings.settings.find(s => s.key === 'labs');
+let configSettings = responseFixtures.config.config;
+
+if (configSettings) {
+    configSettings.labs = defaultLabFlags;
+}
+
+if (!labsSetting) {
+    // If 'labs' key doesn't exist, create it
+    responseFixtures.settings.settings.push({
+        key: 'labs',
+        value: JSON.stringify(defaultLabFlags)
+    });
+} else {
+    // If 'labs' key exists, update its value
+    labsSetting.value = JSON.stringify(defaultLabFlags);
+}
+
+interface LabsSettings {
+    [key: string]: boolean;
+}
+
+export function toggleLabsFlag(flag: string, value: boolean) {
+    // Update responseFixtures.settings
+    labsSetting = responseFixtures.settings.settings.find(s => s.key === 'labs');
+
+    if (!labsSetting) {
+        throw new Error('Labs settings not found');
+    }
+
+    if (typeof labsSetting.value !== 'string') {
+        throw new Error('Labs settings value is not a string');
+    }
+
+    let labs: LabsSettings;
+    try {
+        labs = JSON.parse(labsSetting.value);
+    } catch (e) {
+        throw new Error('Failed to parse labs settings');
+    }
+
+    labs[flag] = value;
+    labsSetting.value = JSON.stringify(labs);
+
+    // Update responseFixtures.config
+    configSettings = responseFixtures.config.config;
+
+    if (configSettings && configSettings.labs) {
+        configSettings.labs[flag] = value;
+    } else {
+        throw new Error('Config settings or labs settings in config not found');
+    }
+}
+
 export const globalDataRequests = {
     browseSettings: {method: 'GET', path: /^\/settings\/\?group=/, response: responseFixtures.settings},
     browseConfig: {method: 'GET', path: '/config/', response: responseFixtures.config},