Re-use common logic for addons purchase

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR refactors the add-on purchases component in order to bring shared logic and templating to one place. The benefit is that of reducing maintenance costs and avoiding unnecessary duplication. In a following iteration, the config options will be provided by the data layer (GraphQL).

Please note that this MR has o visual changes. Screenshots are provided in order to verify consistency with the current layout.

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