Rename Chat Model Options table to Chat Model as short & readable (#1003)

- Previous was incorrectly plural but was defining only a single model
- Rename chat model table field to name
- Update documentation
- Update references functions and variables to match new name

tests/test_offline_chat_actors.py

@@ -2,12 +2,12 @@ from datetime import datetime
 
 import pytest
 
-from khoj.database.models import ChatModelOptions
+from khoj.database.models import ChatModel
 from khoj.routers.helpers import aget_data_sources_and_output_format
 from khoj.utils.helpers import ConversationCommand
 from tests.helpers import ConversationFactory, generate_chat_history, get_chat_provider
 
-SKIP_TESTS = get_chat_provider(default=None) != ChatModelOptions.ModelType.OFFLINE
+SKIP_TESTS = get_chat_provider(default=None) != ChatModel.ModelType.OFFLINE
 pytestmark = pytest.mark.skipif(
     SKIP_TESTS,
     reason="Disable in CI to avoid long test runs.",