Update Fitbit integration to allow UI based configuration

[allenporter]

Proposed change

Update Fitbit integration to allow UI based configuration entries.

Given the existing features, this is a larger PR than I was hoping. This could be split into smaller PRs if we didn't have to worry about backwards compatibility with existing configuration. Open to suggestions for how to make this smaller.

The authentication system has been reworked to use application credentials. See the Fitbit Developer Guide: Authorization for details on the authentication.

The old approach was configured with these steps:

• Add the platform sensor configuration in yaml
• From the UI, enter the configurator flow. The step was to manually enter credentials into a fitbit.conf file.
• The UI then redirects you to fitbit to authorize, and the integration refreshes the credentials in fitbit.conf.

This change will import credentials into application credentials if they already exist.

The existing settings for which entities to add, clock format, and units are imported automatically. For new integrations, the entities to include are now automatically determined based on the allowed scopes enabled by the user.

TODO: Link to documentation

This is pulled out of a larger overhaul to modernize the fitbit integration and make it configurable from the UI and following current design standards, similar to previous approach on Google calendar :

• Add test harness Add tests for fitbit integration #100765
• Add myself as a fitbit codeowner #100766
• Increase test coverage Add more test coverage for fitbit sensors #100776
• Simplify response parsing and entity descriptions Rewrite fitbit sensor API response value parsing #100782
• Refactor unit system Simplify fitbit unit system and conversions #100825
• Ascynio client library Update fitbit client to use asyncio #100933
• Config flow and UI based configuration, application credentials, import of existing credentials Update Fitbit integration to allow UI based configuration #100897
• Reauth support in config flow Add reauth support in fitbit #101178
• Additional oauth error handling with improved error messages in the UI Update fitbit error handling #101304
• Split battery device level into another entity
• Modernize entities to current design standards (battery, time, etc) Modernize fitbit sensors #101179

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: Add documentation for fitbit UI configuration flows home-assistant.io#29025

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
• I have followed the perfect PR recommendations
• 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.

To help with the load of incoming pull requests:

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

[allenporter]

Thanks for the review. I improved test coverage to try to make some of the checks happier as well.

Now this PR is looking for additional input on the import config flow to make sure we're coverage the cases right. Reviewers, check out the config flow tests to see what the cases look like.

[allenporter]

There is a codecov check that appears incorrect. deprecated_yaml_import_issue_cannot_connect is definitely covered by tests that assert on the issue and reason. (I don't want to force push, though, to make review harder)

[MartinHjelmare]

Nice!

Addressed feedback