[Admin] Tweaks for the product listing

[waiting-for-dev]

Summary

Please, see individual commits for details:

• Inject components into the products index one [Admin] component instance variables #5254
• Make product columns more easily customizable
• Move model plural name to a helper
• Use a component for columns in tables (removed, it was a data cell component that didn't fit in the updated code)
• Make clear that the component product methods are public and customizable [Admin] Adjust method visibility in the products/index component #5245

Ref. #5174

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[waiting-for-dev]

We decided to integrate the changes in work that have been done on top of the product listing. "Use a component for columns in tables" will be left out for now.

Keeping open as reference.

[elia]

I rebased on the updated dev-branch, skipped the column component which didn't apply well to the updated code.