Add config flow to mystrom

[pail23]

Breaking change

The YAML configuration will be deprecated.

Proposed change

Add config flow for mystrom switches and bulbs

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

The integration reached or maintains the following Integration Quality Scale:

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To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[probot-home-assistant]

Hey there @fabaff, mind taking a look at this pull request as it has been labeled with an integration (mystrom) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[github-actions]

There hasn't been any activity on this pull request recently. This pull request has been automatically marked as stale because of that and will be closed if no further activity occurs within 7 days.
Thank you for your contributions.

[bdraco]

Looks like there is a conflict that needs to be resolved

[github-actions]

There hasn't been any activity on this pull request recently. This pull request has been automatically marked as stale because of that and will be closed if no further activity occurs within 7 days.
Thank you for your contributions.

[OneCyrus]

would be great if this PR doesn't die and gets a review again.

[phedoreanu]

@bdraco what about another review and a merge? 😁

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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[epenet]

Last couple of comments have not been adressed.

[pail23]

@epenet I hope now I catched all your comments

[epenet]

Last set of changes, then good to go.

[pail23]

I have merged your proposals. Many thanks for your help!

[epenet]

LGTM

[epenet]

Aaarrgh ! just realised this is missing a documentation PR.
@pail23 can you please open the corresponding doc PR?

[pail23]

@epenet I have created home-assistant/home-assistant.io#27667