Add default_config component (#20799)

* Add default config component

* Add default_config to default config

* Fix comments

tests/components/default_config/test_init.py

@@ -0,0 +1,27 @@
+"""Test the default_config init."""
+from unittest.mock import patch
+
+from homeassistant.setup import async_setup_component
+
+import pytest
+
+from tests.common import MockDependency
+
+
+@pytest.fixture(autouse=True)
+def netdisco_mock():
+    """Mock netdisco."""
+    with MockDependency('netdisco', 'discovery'):
+        yield
+
+
+@pytest.fixture(autouse=True)
+def recorder_url_mock():
+    """Mock recorder url."""
+    with patch('homeassistant.components.recorder.DEFAULT_URL', 'sqlite://'):
+        yield
+
+
+async def test_setup(hass):
+    """Test setup."""
+    assert await async_setup_component(hass, 'default_config', {})