feat(core): support ai network search (#9357)

### What Changed?
- Add `PerplexityProvider` in backend.
- Update session prompt name if user toggle network search mode in chat panel.
- Add experimental flag for AI network search feature.
- Add unit tests and e2e tests.

Search results are streamed and appear word for word:

<div class='graphite__hidden'>
          <div>🎥 Video uploaded on Graphite:</div>
            <a href="https://app.graphite.dev/media/video/sJGviKxfE3Ap685cl5bj/56f6ec7b-4b21-405f-9612-43e083f6fb84.mov">
              <img src="https://app.graphite.dev/api/v1/graphite/video/thumbnail/sJGviKxfE3Ap685cl5bj/56f6ec7b-4b21-405f-9612-43e083f6fb84.mov">
            </a>
          </div>
<video src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/sJGviKxfE3Ap685cl5bj/56f6ec7b-4b21-405f-9612-43e083f6fb84.mov">录屏2024-12-27 18.58.40.mov</video>

Click the little globe icon to manually turn on/off Internet search:
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          <div>🎥 Video uploaded on Graphite:</div>
            <a href="https://app.graphite.dev/media/video/sJGviKxfE3Ap685cl5bj/778f1406-bf29-498e-a90d-7dad813392d1.mov">
              <img src="https://app.graphite.dev/api/v1/graphite/video/thumbnail/sJGviKxfE3Ap685cl5bj/778f1406-bf29-498e-a90d-7dad813392d1.mov">
            </a>
          </div>
<video src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/sJGviKxfE3Ap685cl5bj/778f1406-bf29-498e-a90d-7dad813392d1.mov">录屏2024-12-27 19.01.16.mov</video>

When there is an image, it will automatically switch to the openai model:

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          <div>🎥 Video uploaded on Graphite:</div>
            <a href="https://app.graphite.dev/media/video/sJGviKxfE3Ap685cl5bj/56431d8e-75e1-4d84-ab4a-b6636042cc6a.mov">
              <img src="https://app.graphite.dev/api/v1/graphite/video/thumbnail/sJGviKxfE3Ap685cl5bj/56431d8e-75e1-4d84-ab4a-b6636042cc6a.mov">
            </a>
          </div>
<video src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/sJGviKxfE3Ap685cl5bj/56431d8e-75e1-4d84-ab4a-b6636042cc6a.mov">录屏2024-12-27 19.02.13.mov</video>

packages/backend/server/tests/copilot.e2e.ts

@@ -16,6 +16,7 @@ import {
   CopilotProviderService,
   FalProvider,
   OpenAIProvider,
+  PerplexityProvider,
   registerCopilotProvider,
   unregisterCopilotProvider,
 } from '../src/plugins/copilot/providers';
@@ -41,6 +42,7 @@ import {
   sse2array,
   textToEventStream,
   unsplashSearch,
+  updateCopilotSession,
 } from './utils/copilot';
 
 const test = ava as TestFn<{
@@ -63,6 +65,9 @@ test.beforeEach(async t => {
             fal: {
               apiKey: '1',
             },
+            perplexity: {
+              apiKey: '1',
+            },
             unsplashKey: process.env.UNSPLASH_ACCESS_KEY || '1',
           },
         },
@@ -91,6 +96,7 @@ test.beforeEach(async t => {
 
   unregisterCopilotProvider(OpenAIProvider.type);
   unregisterCopilotProvider(FalProvider.type);
+  unregisterCopilotProvider(PerplexityProvider.type);
   registerCopilotProvider(MockCopilotTestProvider);
 
   await prompt.set(promptName, 'test', [
@@ -156,6 +162,85 @@ test('should create session correctly', async t => {
   }
 });
 
+test('should update session correctly', async t => {
+  const { app } = t.context;
+
+  const assertUpdateSession = async (
+    sessionId: string,
+    error: string,
+    asserter = async (x: any) => {
+      t.truthy(await x, error);
+    }
+  ) => {
+    await asserter(updateCopilotSession(app, token, sessionId, promptName));
+  };
+
+  {
+    const { id: workspaceId } = await createWorkspace(app, token);
+    const docId = randomUUID();
+    const sessionId = await createCopilotSession(
+      app,
+      token,
+      workspaceId,
+      docId,
+      promptName
+    );
+    await assertUpdateSession(
+      sessionId,
+      'should be able to update session with cloud workspace that user can access'
+    );
+  }
+
+  {
+    const sessionId = await createCopilotSession(
+      app,
+      token,
+      randomUUID(),
+      randomUUID(),
+      promptName
+    );
+    await assertUpdateSession(
+      sessionId,
+      'should be able to update session with local workspace'
+    );
+  }
+
+  {
+    const aToken = (await signUp(app, 'test', 'test@affine.pro', '123456'))
+      .token.token;
+    const { id: workspaceId } = await createWorkspace(app, aToken);
+    const inviteId = await inviteUser(
+      app,
+      aToken,
+      workspaceId,
+      'darksky@affine.pro'
+    );
+    await acceptInviteById(app, workspaceId, inviteId, false);
+    const sessionId = await createCopilotSession(
+      app,
+      token,
+      workspaceId,
+      randomUUID(),
+      promptName
+    );
+    await assertUpdateSession(
+      sessionId,
+      'should able to update session after user have permission'
+    );
+  }
+
+  {
+    const sessionId = '123456';
+    await assertUpdateSession(sessionId, '', async x => {
+      await t.throwsAsync(
+        x,
+        { instanceOf: Error },
+        'should not able to update invalid session id'
+      );
+    });
+  }
+});
+
 test('should fork session correctly', async t => {
   const { app } = t.context;