More typing (#15449)

## Description:

More typing improvements.

Switch to using `mypy.ini` for flexibility

Add `warn_return_any` check except in `homeassistant.util.yaml` that does typing hacks. Fix some type annotations as resulting from this check and ignore others were fixing is hard.

## Checklist:
  - [x] The code change is tested and works locally.
  - [x] Local tests pass with `tox`. **Your PR cannot be merged unless tests pass**

homeassistant/util/json.py

@@ -25,7 +25,7 @@ def load_json(filename: str, default: Union[List, Dict, None] = None) \
     """
     try:
         with open(filename, encoding='utf-8') as fdesc:
-            return json.loads(fdesc.read())
+            return json.loads(fdesc.read())  # type: ignore
     except FileNotFoundError:
         # This is not a fatal error
         _LOGGER.debug('JSON file not found: %s', filename)