Migrate geo_json_events to config flow

[exxamalte]

Proposed change

Migrate geo_json_events to config flow, including automated migration of YAML configuration.

That's it - no new diagnostics sensor, no migration to coordinator, no deprecation of scan_interval, that will all follow in later PRs.

This PR replaces https://github.com/home-assistant/core/pull/70439 and is strictly limited to the minimum of migrating to config flow.

Type of change

• [ ] Dependency upgrade
• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] New integration (thank you!)
• [x] 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: https://github.com/home-assistant/home-assistant.io/pull/22471

Checklist

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

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

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

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

• [x] 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.

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[epenet]

Note: please add a breaking-change section at the top of the PR description.

[exxamalte]

Based on latest comments regarding the scan interval, it needs to be fully taken out from config flow.

Just to avoid any misunderstandings:

• I remove the option for the user to configure the scan interval in the config flow form when configuring this integration. Instead I choose a fixed scan interval.
• However, when importing the legacy YAML configuration (which currently does support defining a custom scan interval) inside the config flow I carry the configured scan interval over into the new configuration.

[epenet]

Based on latest comments regarding the scan interval, it needs to be fully taken out from config flow.

Just to avoid any misunderstandings:

• I remove the option for the user to configure the scan interval in the config flow form when configuring this integration. Instead I choose a fixed scan interval.
• However, when importing the legacy YAML configuration (which currently does support defining a custom scan interval) inside the config flow I carry the configured scan interval over into the new configuration.

No, it shouldn't be imported.

[exxamalte]

Thank you very much for your help and support getting through this PR!