[V3 Config] Implement a true clear method (#1344)

* Add clear methods to drivers

* Update config clear methods, add to Value

* Add test

tests/core/test_config.py

@@ -298,6 +298,16 @@ async def test_member_clear_all(config, member_factory):
     assert len(await config.all_members()) == 0
 
 
+@pytest.mark.asyncio
+async def test_clear_value(config_fr):
+    config_fr.register_global(foo=False)
+    await config_fr.foo.set(True)
+    await config_fr.foo.clear()
+
+    with pytest.raises(KeyError):
+        await config_fr.get_raw('foo')
+
+
 # Get All testing
 @pytest.mark.asyncio
 async def test_user_get_all_from_kind(config, user_factory):