Move registry engine config from core config to its engine

[jesusbv]

Move registry cache declaration for testing into the right engine

Description

Move Registry engine config from core to its engine Move registry cache directory declaration to the right engine

Fixes # (issue)

Change Type

Please select the correct option.

• [ ] Bug Fix (a non-breaking change which fixes an issue)
• [x] New Feature (a non-breaking change which adds new functionality)
• [ ] Documentation Update (a change which only updates documentation)

Checklist

Please check off each item if the requirement is met.

• [x] I have verified that my code follows RMT's coding standards with rubocop.
• [x] I have reviewed my own code and believe that it's ready for an external review.
• [x] I have provided comments for any hard-to-understand code.
• [ ] I have documented the MANUAL.md file with any changes to the user experience.
• [x] RMT's test coverage remains at 100%.
• [ ] If my changes are non-trivial, I have added a changelog entry to notify users at package/obs/rmt-server.changes.

Other Notes

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