Add/module products

[leogermani]

Adds the backend for Module Products

Changes proposed in this Pull Request:

• Adds the backend for Module Products

Jetpack product discussion

p9dueE-4g1-p2

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Watch tests
• Look at code
• Try to activate/deactivate one of these products via REST API?

[github-actions]

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[retrofox]

Leaving a note, modules like scan require additional settings:

When I try to activate it, I get the following error:

Another good reason to keep with the same single product management path,

[retrofox]

I think in general we should add an array( 'status' => XXX ) as the third parameter of the error instance. It will help to deal with the errors on the client-side.
For instance, when I try to activate the scan product I gen an error which is expected (comment here). However, the error status code is 500 from the request, and it doesn't contain any status in its response (data null).

I wonder if we can use one of the standard codes when it fails.
In this case, may we use 401?

[leogermani]

Sure! This should be handled by the REST API endpoint. Let's address this in another PR

[retrofox]

ok, it can get trickier from there since we'll have to check the type of error before populating the error.
Generally, it just checks if is_wp_error(). If so, it just sends the error to the client.

[retrofox]

Left a comment about response error, we can polish it in follow-up PRs, though.
It works as expcted. I could activate/deactivate the VideoPress module from My Jetpack properly.
LGTM.