Summary:
This is just refactoring in preparation to open-sourcing internal plugin distribution code to make it available for other orgs so they can distribute their internal plugins. See other diffs in the same stack.
This diff moves recommended plugins handling from `pluginMarketplace` which will be the same for fb-internal and OS versions into `pluginMarketplaceAPI` which will differ for fb-internal and OS versions. This will make it possible for other orgs to define their own "recommended" plugins which then will be automatically installed/enabled for new users.
Reviewed By: aigoncharov
Differential Revision: D34379981
fbshipit-source-id: 5c3a4efb6d0171256cf508f9005d914d7332e14f
