Add a helpful message to the config_entries.OperationNotAllowed exception

[bdraco]

Proposed change

We only expect this exception to be raised as a result of an implementation problem. When it is raised during production it is currently hard to trace down why its happening

See #75835

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 #
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[bdraco]

Tagging for a patch so we can hopefully figure out why #75835 is happening

[bdraco]

Thanks