Move tutorials api in src/legacy/core_plugins/kibana/server/routes/api/home to the new platform.
The most important part is the registry where plugins can register new tutorials(src/legacy/ui/tutorials_mixin.js). This is where the main effort lies.

The following methods need to be returned from the new TutorialsPlugin setup method:
getTutorials, registerTutorial and addScopedTutorialContextFactory.
At the moment, the methods accept the main kbn server and request objects. Once the server and request are not explicitly called, we'll be able to migrate the decoration methods to a new Tutorials plugin.