Use ProviderManager in reconciler

[dmjb]

Relates to #2845

Part of the ongoing decoupling of Provider-specific details from various parts of Minder.

Summary

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Fixes #(related issue)

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• Bug fix (resolves an issue without affecting existing features)
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Review Checklist:

• Reviewed my own code for quality and clarity.
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[coveralls]

coverage: 50.097% (+0.04%) from 50.056%
when pulling c3b009d on reconcilers-provider-manager
into 7fc9740 on main.