[Multi-User Part 2]: Add login pages and gate access to application behind login wall (#503)

- Make most routes conditional on authentication *if anonymous mode is not enabled*. If anonymous mode is enabled, it scaffolds a default user and uses that for all application interactions.
- Add a basic login page and add routes for redirecting the user if logged in

tests/conftest.py

@@ -25,7 +25,6 @@ from khoj.utils.rawconfig import (
     OfflineChatProcessorConfig,
     OpenAIProcessorConfig,
     ProcessorConfig,
-    TextContentConfig,
     ImageContentConfig,
     SearchConfig,
     TextSearchConfig,
@@ -38,7 +37,6 @@ from database.models import (
     LocalOrgConfig,
     LocalMarkdownConfig,
     LocalPlaintextConfig,
-    LocalPdfConfig,
     GithubConfig,
     KhojUser,
     GithubRepoConfig,
@@ -95,6 +93,19 @@ def default_user():
     return UserFactory()
 
 
+@pytest.mark.django_db
+@pytest.fixture
+def default_user2():
+    if KhojUser.objects.filter(username="default").exists():
+        return KhojUser.objects.get(username="default")
+
+    return UserFactory(
+        username="default",
+        email="default@example.com",
+        password="default",
+    )
+
+
 @pytest.fixture(scope="session")
 def search_models(search_config: SearchConfig):
     search_models = SearchModels()