Nest config flow (#14921)

* Move nest to dir based component

* Add config flow for Nest

* Load Nest platforms via config entry

* Add tests for Nest config flow

* Import existing access tokens as config entries

* Lint

* Update coverage

* Update translation

* Fix tests

* Address strings

* Use python-nest token resolution

* Lint

* Do not do I/O inside constructor

* Lint

* Update test requirements

script/gen_requirements_all.py

@@ -77,6 +77,7 @@ TEST_REQUIREMENTS = (
     'pynx584',
     'pyqwikswitch',
     'python-forecastio',
+    'python-nest',
     'pytradfri\[async\]',
     'pyunifi',
     'pyupnp-async',