Add Growatt Server Config flow (#41303)

* Growatt Server Config flow

* Use reference strings

Co-authored-by: SNoof85 <snoof85@gmail.com>

* Remove configuration.yaml import logic

* Removed import test

* Re-added PLATFORM_SCHEMA validation

* Import yaml from old yaml configuration

* Apply suggestions from code review

Co-authored-by: Martin Hjelmare <marhje52@gmail.com>

* Feedback

* Use Executor for IO only

* Fix imports

* update requirements

* Fix flake8

* Run every section of fetching devices in single executor

* Config flow feedback

* Clean up

* Fix plan step

* Fix config flow test

* Remove duplicate test

* Test import step

* Test already configured entry

* Clean up tests

* Add asserts

* Mock out entry setup

* Add warning if set up via yaml

Co-authored-by: SNoof85 <snoof85@gmail.com>
Co-authored-by: Martin Hjelmare <marhje52@gmail.com>