Introduce mux and port the provider to v6.

[dimuon]

Description

Port existing provider to v6.
It should allow us to

• create a new provider
• port data sources and resources to the new provider
• once all data sources and resources are ported, we can remove mux.

The approach should allow us to keep almost the full functionality of the provider available during the migration process.

Related Issues

Motivation and Context

How Has This Been Tested?

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (improves code quality but has no user-facing effect)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation

Readiness Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

[pascal-hofmann]

Awesome. This looks really good and will make a transition to the framework very smooth. I'll rebase my changes on your code once it's merged.