[Multi-User Part 4]: Authenticate using API Tokens (#513)

### ✨ New
- Use API keys to authenticate from Desktop, Obsidian, Emacs clients
- Create API, UI on web app config page to CRUD API Keys
- Create user API keys table and functions to CRUD them in Database

### 🧪 Improve
- Default to better search model, [gte-small](https://huggingface.co/thenlper/gte-small), to improve search quality
- Only load chat model to GPU if enough space, throw error on load failure
- Show encoding progress, truncate headings to max chars supported
- Add instruction to create db in Django DB setup Readme

### ⚙️ Fix
- Fix error handling when configure offline chat via Web UI
- Do not warn in anon mode about Google OAuth env vars not being set
- Fix path to load static files when server started from project root

src/database/models/__init__.py

@@ -37,6 +37,15 @@ class GoogleUser(models.Model):
         return self.name
 
 
+class KhojApiUser(models.Model):
+    """User issued API tokens to authenticate Khoj clients"""
+
+    user = models.ForeignKey(KhojUser, on_delete=models.CASCADE)
+    token = models.CharField(max_length=50, unique=True)
+    name = models.CharField(max_length=50)
+    accessed_at = models.DateTimeField(null=True, default=None)
+
+
 class NotionConfig(BaseModel):
     token = models.CharField(max_length=200)
     user = models.ForeignKey(KhojUser, on_delete=models.CASCADE)