Make API key mandatory for PI-Hole

[mib1185]

Proposed change

Since pi-hole version 5.18, the API key is mandatory (home-assistant-ecosystem/python-hole#13) for every api call. This has been implemented with #84516 in HA, but the config flow was never adjusted accordingly and no config entry migration has been done.
This PR will remove the config option CONF_STATISTICS_ONLY which was the condition if user is asked for api key or not.
Further CONF_STATISTICS_ONLY is now removed from any existing configuration entry and a missing CONF_API_KEY will start the reauth flow (yes it is a new feature, but it is a requirement for this bug fix).

With this it is ensured, that every PI-Hole configuration entry has a valid api key.

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: pi-hole broken after updating pi-hole web to 5.18 #84422
• Link to documentation pull request: make api key mandatory for PI-hole home-assistant.io#25585

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

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• The manifest file has all fields filled out correctly.
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• 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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[home-assistant]

Hey there @johnluetke, @shenxn, mind taking a look at this pull request as it has been labeled with an integration (pi_hole) you are listed as a code owner for? Thanks!

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[MartinHjelmare]

Thanks!

[balloob]

I'm unable to cherry-pick this PR due to it being created on top of #84803, which is a breaking change and should not be picked into a hot fix.

If you want this fix in a hot fix, open a new PR with the change against rc.

[mib1185]

I'm unable to cherry-pick this PR due to it being created on top of #84803, which is a breaking change and should not be picked into a hot fix.

If you want this fix in a hot fix, open a new PR with the change against rc.

have done so in #85885