feat(server): add fallback model and baseurl in schema (#13375)

fix AI-398

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Added support for specifying fallback models for multiple AI
providers, enhancing reliability when primary models are unavailable.
* Providers can now fetch and update their list of available models
dynamically from external APIs.
* Configuration options expanded to allow custom base URLs for certain
providers.

* **Bug Fixes**
* Improved model selection logic to use fallback models if the requested
model is not available online.

* **Chores**
* Updated backend dependencies to include authentication support for
Google services.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/config.ts

@@ -47,6 +47,13 @@ defineModuleConfig('copilot', {
     desc: 'The config for the openai provider.',
     default: {
       apiKey: '',
+      baseUrl: '',
+      fallback: {
+        text: '',
+        structured: '',
+        image: '',
+        embedding: '',
+      },
     },
     link: 'https://github.com/openai/openai-node',
   },
@@ -60,28 +67,54 @@ defineModuleConfig('copilot', {
     desc: 'The config for the gemini provider.',
     default: {
       apiKey: '',
+      baseUrl: '',
+      fallback: {
+        text: '',
+        structured: '',
+        image: '',
+        embedding: '',
+      },
     },
   },
   'providers.geminiVertex': {
     desc: 'The config for the gemini provider in Google Vertex AI.',
-    default: {},
+    default: {
+      baseURL: '',
+      fallback: {
+        text: '',
+        structured: '',
+        image: '',
+        embedding: '',
+      },
+    },
     schema: VertexSchema,
   },
   'providers.perplexity': {
     desc: 'The config for the perplexity provider.',
     default: {
       apiKey: '',
+      fallback: {
+        text: '',
+      },
     },
   },
   'providers.anthropic': {
     desc: 'The config for the anthropic provider.',
     default: {
       apiKey: '',
+      fallback: {
+        text: '',
+      },
     },
   },
   'providers.anthropicVertex': {
     desc: 'The config for the anthropic provider in Google Vertex AI.',
-    default: {},
+    default: {
+      baseURL: '',
+      fallback: {
+        text: '',
+      },
+    },
     schema: VertexSchema,
   },
   'providers.morph': {